This article examines the doctrine of the Holy Trinity in eleven sections, with special attention to the Catechism of the Catholic Church (CCC) and a foundation in the theology of St. Thomas Aquinas. The subdivisions of this article are:

I. The Doctrine of the Trinity 
II. The Trinity in Scripture 
III. The Trinity in the Early Church 
IV. The Analogy of the Word and Love 
V. The Father and the Son 
VI. The Son and the Holy Spirit 
VII. Relations in the Trinity 
VIII. The Missions of the Divine Persons
IX. Appropriation 
X. Knowledge of the Trinity as Necessary for Salvation
XI The Real Effect of this Doctrine on Our Lives

I. The Doctrine of the Trinity

Christians confess the Trinity—three really distinct persons in one numerically same God—because Jesus Christ, our Savior, has revealed this mystery to us. Two paragraphs of the Catechism of the Catholic Church (CCC) articulate these two aspects of oneness and real distinction in Christ’s teaching:

<em>The Trinity is One.</em> We do not confess three Gods, but one God in three persons, the “consubstantial Trinity.” The divine persons do not share the one divinity among themselves but each of them is God whole and entire: “The Father is that which the Son is, the Son that which the Father is, the Father and the Son that which the Holy Spirit is, i.e. by nature one God.” In the words of the Fourth Lateran Council (1215), “Each of the persons is that supreme reality, viz., the divine substance, essence or nature.” (<em>CCC</em> no. 253, emphasis in original)

<em>The divine persons are really distinct from one another.</em> “God is one but not solitary.” “Father,” “Son,” “Holy Spirit” are not simply names designating modalities of the divine being, for they are really distinct from one another: “He is not the Father who is the Son, nor is the Son he who is the Father, nor is the Holy Spirit he who is the Father or the Son.” They are distinct from one another in their relations of origin: “It is the Father who generates, the Son who is begotten, and the Holy Spirit who proceeds.” The divine Unity is Triune. (<em>CCC</em> no. 254, emphasis in original)

Why does CCC no. 253 say “consubstantial” Trinity? This is because the Son and the Holy Spirit are consubstantial with the Father; that is, they have the very same substance or essence as the Father—and each other. That is why they do not “share” the divine essence; each is essentially the divine essence. If someone shares in something, he is not essentially whatever it is that he shares. Rather, he participates in what is shared. For instance, I participate in existence; I am not simply the fullness of existence itself. By contrast, each divine person is essentially the divine essence.

On the point of oneness, CCC no. 200 reminds us that as “the confession of God’s oneness . . . has its roots in the divine revelation of the Old Covenant,” so “the Christian faith confesses that God is one in nature, substance and essence.” And this unicity of God reflected in our prayers, as “Christians are baptized in the name of the Father and of the Son and of the Holy Spirit: not in their names, for there is only one God, the almighty Father, his only Son and the Holy Spirit: the Most Holy Trinity” (CCC no. 233, emphasis in original). 

Understanding that God is a communion of three persons in no way compromises His perfect unity. Christians declare God’s perfect oneness no less than Muslims or Jews. The assertion that God is a communion of three persons—the Father, the Son, and the Holy Spirit—does not affect God’s perfect unity in the least. It is not an “either-or” but a “both-and.” If the idea of three persons makes us lose track of the one God with one being, one divine essence, one life, one intellect, and one will, then we have lost Christian teaching. A non-Christian might not think that it is possible for the one God to be a communion of three persons, but he should not think that Christians doubt that there is one God, or that God is perfectly one.

Why does CCC no. 254 say “really distinct”? This is because the divine persons are not distinct only in our minds according to different perspectives. That is, it is not like considering your cousin as your relative versus as your friend versus as your bowling partner versus as your dentist, when the same person is in fact all of these things. The divine persons are distinct, not only in the logical order, but in the real order as well. The reference to distinction merely by “modalities” concerns the heresy of Sabellianism, which we describe below in the section on the Trinity in the early Church. We also discuss distinction by relations of origin below in the section on relations in the Trinity.

This saving truth of God as a Trinity is so central to the Christian faith, that we profess it out loud at Mass and at Baptisms. As CCC no. 232 reminds us:

Christians are baptized “in the name of the Father and of the Son and of the Holy Spirit” (Mt 28:19). Before receiving the sacrament, they respond to a three-part question when asked to confess the Father, the Son and the Spirit: “I do.” “The faith of all Christians rests on the Trinity.” 

And as CCC no. 234 affirms, because this a revelation about God’s very nature, it is the central mystery of the faith and the source of all of the other mysteries; and it should not be disconnected from God’s work of salvation in the created order:

The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the “hierarchy of the truths of faith.” The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men “and reconciles and unites with himself those who turn away from sin.”

Our Knowledge about God

Even by reason alone, without faith, it is possible to know that a God exists and that there is only one God. Indeed, in his letter to the Romans, St. Paul calls out unbelief as unjustified: “Ever since the creation of the world his invisible nature, namely, his eternal power and deity, has been clearly perceived in the things that have been made. So they [the unbelievers] are without excuse” (Rom 1:20). Furthermore, Vatican I’s Dei Filius, Canon II.1 declares: “If anyone shall say that the One True God, our Creator and Lord, cannot be certainly known by the natural light of human reason through created things, let him be anathema.” And CCC no. 286 reprises this teaching:

Human intelligence is surely already capable of finding a response to the question of origins. The existence of God the Creator can be known with certainty through his works, by the light of human reason, even if this knowledge is often obscured and disfigured by error. This is why faith comes to confirm and enlighten reason in the correct understanding of this truth: “By faith we understand that the world was created by the word of God, so that what is seen was made out of things which do not appear.”

By contrast, one can only know that God is a Trinity by divine revelation. That is, if God did not reveal that fact to us through Jesus, we would never have known it:

The Trinity is a mystery of faith in the strict sense, one of the “mysteries that are hidden in God, which can never be known unless they are revealed by God.” To be sure, God has left traces of his Trinitarian being in his work of creation and in his Revelation throughout the Old Testament. But his inmost Being as Holy Trinity is a mystery that is inaccessible to reason alone or even to Israel’s faith before the Incarnation of God’s Son and the sending of the Holy Spirit. (<em>CCC</em> no. 237)

Moreover, to accept this revelation as true requires faith in God who is speaking to us because His divine manner of existing as three distinct persons in one same God exceeds our mental grasp. There is nothing in the created order that is like this, so we have nothing to see with our eyes and picture in our imaginations to allow our minds to rest in peaceful comprehension. Vatican I’s Dei Filius defends this truth in Canon IV.1: “If anyone shall say that, in Divine Revelation, there are no mysteries, truly and properly so-called, but that all of the doctrines of faith can be understood and demonstrated from natural principles, by properly-cultivated reason, let him be anathema.”

Our Speech about God

Although our knowledge and speech about God is infinitely inadequate, what we know and say is still true—or false; that is, we are not just babbling irrelevantly. We can have correct ideas and make true assertions about God, and we can have incorrect ideas and make false assertions about God. God reveals himself to us through human language, and our words are ordered to signifying created things. So, when we apply words to God, the words are taken from created things, but they are applied by analogy to God. When we say “by analogy,” we understand that there is a real similarity between God and us—not just an imagined similarity that we capitalize on linguistically. The dissimilarity between God and any creature is infinite. We are more dissimilar to God than we are similar. But still, there is a real similarity between God, who causes us to be, and us, who are his effects. He truly acts as efficient cause in creating us, so there is a real resemblance between us and God.

Thus, when we say that God is good, we speak properly and not just metaphorically. When we say “Father,” “Son,” and “Holy Spirit,” we again speak properly on the strength of analogy. These names, taken from creatures, apply to God first of all. God is the prime analogate of all absolute perfections in the created universe. Consequently, as weak as the created universe is in reflecting God’s being, it does really reflect him—and not just in our imaginations. That is, it gives true knowledge of God, despite its infinite inferiority to God. Therefore, human language, which is based on created reality, can successfully signify God himself, not just our ideas about God. This makes it possible for us to receive a true revelation of God in human language. Indeed, there is no other way for us to receive a revelation. If the revelation is to usso that we can grasp it, then it must be in a human mode. CCC no. 236 touches on this theme in affirming that theology is revealed in the economy:

The Fathers of the Church distinguish between theology (<em>theologia</em>) and economy (<em>oikonomia</em>). “Theology” refers to the mystery of God’s inmost life within the Blessed Trinity and “economy” to all the works by which God reveals himself and communicates his life. Through the <em>oikonomia</em> the <em>theologia</em> is revealed to us; but conversely, the <em>theologia</em> illuminates the whole <em>oikonomia</em>. God’s works reveal who he is in himself; the mystery of his inmost being enlightens our understanding of all his works. So it is, analogously, among human persons. A person discloses himself in his actions, and the better we know a person, the better we understand his actions.

As a consequence, we can trust that when we read that the Father has sent the Son into the world (Jn 5:25 and 10:36; 1 Jn 4:14) and that the Father and the Son have sent the Spirit into the world (Jn 14:26 and 15:26), the order of these “missions” of divine persons reveals to us the order of processions in God. A mission of a divine person refers to the sending of a divine person to be present in a new way in the oikonomia. (“Mission” comes from the Latin verb mittere, which means “to send.”) The visible mission of the Son is Christ in the flesh. The traditionally recognized visible missions of the Spirit are the dove at Christ’s baptism, Christ’s breathing on the apostles when he gave them the power to forgive sins, and the tongues of fire at Pentecost. St. John Damascene and St. Thomas Aquinas include the cloud at the Transfiguration, but most Fathers of the Church do not. In any case, these are visible signs that represent the Spirit and signify His presence when He has been sent by the Father and the Son. The invisible missions of the Son and the Spirit are to angels and men in the gifts of grace, faith and charity.

The Catechism affirms the reality of divine revelation through the created order. The missions reflect the order of processions in God himself:

The eternal origin of the Holy Spirit is revealed in his mission in time. The Spirit is sent to the apostles and to the Church both by the Father in the name of the Son, and by the Son in person, once he had returned to the Father. The sending of the person of the Spirit after Jesus’ glorification reveals in its fullness the mystery of the Holy Trinity. (<em>CCC</em> no. 244) 

We will discuss the divine missions in greater detail below in the section on the divine missions, and we will also say more about our speech about God in the section on the Trinity in the early Church.

II. The Trinity in Scripture

One can encounter a certain skepticism in some quarters about whether this doctrine is clearly taught in the Bible or was even believed by Christians before the fourth century. For instance, the New Catholic Encyclopedia (1967) cautions that “one should not speak of Trinitarianism in the New Testament without serious qualification” since this dogma was not developed until “the last quadrant of the 4th century” (v. 14, p. 295). But we should not lose track of three important pertinent facts: (1) Jesus is truly God the Son, and thus he knew that one God is a communion of three distinct persons; (2) Jesus wished to communicate this truth to us so that we can have true faith in God; and (3) Jesus sent the Holy Spirit upon his Church to guide her teaching and protect her from error. If Jesus is not who he says he is, then we should look for someone else to follow. But if Jesus is our Savior, God in the flesh, the “one mediator between God and men” (1 Tm 2:5), then we should expect to find God reliably revealed in the Bible, and we should expect the Church to be able to interpret the Bible correctly with the help of the Holy Spirit. That is, Christ did not leave us guessing: “In many and various ways God spoke of old to our fathers by the prophets; but in these last days he has spoken to us by a Son” (Heb 1:1-2). God succeeds in His effort to reveal Himself to us through the Scriptures: “So shall my word be that goes forth from my mouth; it shall not return to me empty, but it shall accomplish that which I purpose, and prosper in the thing for which I sent it" (Is 55:11).

In the Gospel, Jesus declares, “I came from the Father” (Jn 16:28). Jesus is “the only Son from the Father,” who is “the Word [that] became flesh and dwelt among us” (Jn 1:14). This Word “was with God [the Father] (ὁ θεὸς)” and “was God (θεὸς)” himself (Jn 1:1). Thus, the Father is not the same person as the Son, for nothing comes forth from itself. There is a Father, and there is a Son, who is not the Father. Yet, they are both God; they are one same God: The “[Son] and the Father are one” (Jn 10:30). 

Not only the Son but also “the Spirit of truth . . . proceeds from the Father” (Jn 15:26). And the Son too sends the Holy Spirit “to [us] from the Father” (Jn 15:26). So, the Holy Spirit is neither the Father nor the Son. Yet he is revealed to be God, since he can comprehend God, which only God can do: “The Spirit searches everything, even the depths of God . . . [and] no one comprehends the thoughts of God except the Spirit of God” (1 Cor 2:10-11).

CCC no. 249 points out not only the early scriptural affirmation of the Trinity in the words of St. Paul, but also the centrality of this revelation to the Christian life. This is the saving truth that the followers of Christ must know and accept:

From the beginning, the revealed truth of the Holy Trinity has been at the very root of the Church’s living faith, principally by means of Baptism. It finds its expression in the rule of baptismal faith, formulated in the preaching, catechesis and prayer of the Church. Such formulations are already found in the apostolic writings, such as this salutation [of St. Paul] taken up in the Eucharistic liturgy: “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.”

III. The Trinity in the Early Church

Theology is faith seeking understanding (Anselm, Proslogion), and two important roles of theology are to elucidate the faith and rule out error (Aquinas, Summa contra Gentiles I, ch. 2). One might wonder how theologians could have developed such detailed descriptions of the Trinity, whose being is so far above our grasp. So often it has been heresies that have forced the Church to find very precise language in order to defend the true faith. There is a tension present to the human mind as it is stretched beyond the orbit of reason by faith in God as One and Three. As is so often the case with divine mysteries, we must retain a “both/and,” and resist slipping into an “either/or.” Each divine person is distinct from the others in the real order, so that the Father is not the Son or the Holy Spirit, and the Son is not the Holy Spirit. Yet each divine person is equally the divine essence. The Son and the Holy Spirit are no less the divine essence than the Father. For instance, omnipotence and love are common to all three persons; they are not proper to any person and thus cannot distinguish one person from another.

Trinitarian heresies arise when the mystery of oneness and threeness is reduced to a problem of oneness versus threeness. If the problem is resolved in favor of oneness, the heresy will be a form of modalism, which was espoused by Sabellius in the early third century. If resolved in favor of threeness, the heresy will be a form of subordinationism, which was the position of Arius in the late third century. Modalism is the idea that there is only one person in God, and this person is named the Father on account of his act of creation, the Son on account of his act of becoming man, and the Holy Spirit on account of his act of sanctifying man. Here there is perfect unity but no distinction of persons in the real order—simply three modes of one person. Subordinationism is the understanding that the Son and the Holy Spirit are less than the Father and not true God. For instance, Arius held that the Father created the Son, who then in turn created the Holy Spirit and the whole universe. Here there are three distinct persons, but they are not all equally God, even if they have some profound share of the Father’s power. These heresies deprive the mystery of its splendor.

Theologians’ act of reflecting on revelation and expressing the truth about the Trinity in human words was indispensable to the work of early Church councils, as CCC nos. 250 and 251 affirm:

During the first centuries the Church sought to clarify her Trinitarian faith, both to deepen her own understanding of the faith and to defend it against the errors that were deforming it. This clarification was the work of the early councils, aided by the theological work of the Church Fathers and sustained by the Christian people’s sense of the faith.

In order to articulate the dogma of the Trinity, the Church had to develop her own terminology with the help of certain notions of philosophical origin: “substance,” “person” or “hypostasis,” “relation” and so on. In doing this, she did not submit the faith to human wisdom, but gave a new and unprecedented meaning to these terms, which from then on would be used to signify an ineffable mystery, “infinitely beyond all that we can humanly understand.”

As human beings, we have no choice but to use human language, and we need not be ashamed of this, for God Himself, in His great mercy, took human flesh to Himself and has instructed us in human language. Furthermore, we are capable of proper predication about God (St. Thomas Aquinas, Summa theologiae [ST] I, q. 13, a. 3); we are not just parsing our own ideas. That is, we are capable of being right or wrong in what we say about God because we succeed in speaking about God and not just about human images for God. 

Our signification can attain God even though He exceeds our understanding infinitely, because created being is analogous to divine being, and our act of judgment is about the real order, not about our ideas. Because our judgment is about the real God, we do not need to produce a concept adequate to God—which we never could—in order to make proper predications about God. We are able to conjure some real intelligibility about God in our minds by knowing created being and goodness because created being and goodness is analogous to divine being and goodness. Why is this analogous and not altogether equivocal? Because God is the cause of creatures. That is why creatures bear a real likeness to God even though they are more dissimilar than similar to God. If a cause has no relation at all to the effect, then it would not be causing anything. So, there is real similarity in being even though the disproportion is infinite. This makes Church councils’ declarations all the more solemn: the truth about God can be definitively declared by the Magisterium assisted and protected by the Holy Spirit.

CCC no. 242 refers to a historically decisive Church council and to a key term that was included in the creed adopted by that council:

Following this apostolic tradition [of recognizing Jesus as the Word that was God and was with the Father as his image, radiance, and stamp of divine nature], the Church confessed at the first ecumenical council at Nicaea (325) that the Son is “consubstantial” (<em>homoousios</em>) with the Father, that is, one only God with him. The second ecumenical council, held at Constantinople in 381, kept this expression in its formulation of the Nicene Creed and confessed “the only-begotten Son of God, eternally begotten of the Father, light from light, true God from true God, begotten not made, consubstantial with the Father.”

Basic doctrinal formulation of the Trinity is worked out definitively by the late fourth century. Landmarks here are the Councils of Nicaea (325) and Constantinople I (381):

The Church uses (I) the term “substance” (rendered also at times by “essence” or “nature”) to designate the divine being in its unity, (II) the term “person” or “hypostasis” to designate the Father, Son and Holy Spirit in the real distinction among them, and (III) the term “relation” to designate the fact that their distinction lies in the relationship of each to the others. (<em>CCC</em> no. 252)

Even as late as 369, St. Athanasius used ousia (essence) and hypostasis as synonyms. After Constantinople I, however, the fluidity of these terms came to an end.

IV. The Analogy of the Word and Love

When faced with the challenge of making sense of divine revelation insofar as humanly possible, we must turn to analogies, which limp but can still be of great use in helping us to begin to imagine how God is a Trinity. Aquinas believed that the analogy of the word and love, proposed by St. Augustine of Hippo, was far and away the soundest and most powerful analogy we have for the Trinity. This analogy takes note of the fact that the soul is an image of the Trinity. When we know and love God in grace, we become miniature images of the Trinity.

This analogy is so relevant because it brings together perfect equality in essence with real distinction among persons. It does this by modeling the two immanent processions that are found in intellectual beings: knowing and loving. The fact that there is a procession guarantees real distinction, because nothing proceeds from itself. And the fact that the procession is immanent guarantees perfect equality in essence, because anything in God is simply the divine essence.

The Word

CCC no. 241 draws our attention to the fact that God the Son is the Word of the Father, and it points out the Word’s character of equality to the Father on account of likeness in image:

For this reason [namely, that Jesus reveals that he is eternally the Son of a Father] the apostles confess Jesus to be the Word: “In the beginning was the Word, and the Word was with God, and the Word was God” (Jn 1:1); as “the image of the invisible God” (Col 1:15); as the “radiance of the glory of God and the very stamp of his nature” (Heb 1:3).

To gain some insight into the Son’s personality, Augustine draws an analogy between a human word and the divine Word. That is, we can learn something about the Father’s Word by examining the word, or concept, that we produce in our intellects in the act of knowing. With the benefit of Aristotelian epistemology, Aquinas develops Augustine’s analogy and perfects its coherence, as follows.

When an animal sees something, a likeness of the thing is in the eye, namely, a representation of the thing, made of light. The thing itself is not in the eye; otherwise, the potential seer would not see at all. The thing is translated into the order of light; it is a stone made of light. Similarly, in intellectual seeing, a likeness of the thing is in the intellect, i.e., a representation of the thing, “made of idea.” The thing itself is not in the intellect, for instance, a stone; that would be impossible because intellect is incorporeal. Here the thing is translated into the order of knowledge; it is a stone “made of knowledge.” 

When we see something, the eye in a sense takes on the form of the thing seen. For instance, if we are looking at a red stone, the eye takes on that form in being united to it in the order of light. Now, in the case of the eye, a corporeal organ, only part of the eye actually becomes the stone’s redness. By contrast, the intellect has no physical parts. When we know something, the intellect becomes that thing in the order of knowledge (Aquinas, De veritate q. 10, a. 2, ad 4). 

How then does this apply to God? God knows all things through Himself. The divine essence is the only adequate object of the divine intellect. So, in knowing Himself (the divine essence), the Father produces in the divine intellect a likeness of what is known. And the Father’s act of knowing is so perfectly and truly productive that the likeness produced is so real, rich, and definitive that the likeness is a whole other living existing self who possesses the divine essence. The likeness cannot be another divine essence, for there can only be one truly infinite divine essence. And the likeness is not a lesser likeness of the divine essence, for then the Son would not be true God. The Son is such a perfect likeness that He is the essence no less than the Father is. The only distinction between the Father and the Son is that the Father speaks and the Word is spoken. The Son is so similar to the Father that He is not a second copy as another God, but is another within the original. 

Thus, the Son is not the Father, because He proceeds from the Father; and He proceeds from the Father by way of likeness—as a word of knowledge in the intellect. And the likeness is so perfect, that the Son is no less than the Father. So, this analogy gives us real distinction between divine persons, perfect equality of essence, and the Son’s personality as the Word: likeness to the Father. This is why the Son so perfectly manifests the Father: “Jesus said to [Philip], ‘Have I been with you so long, and yet you do not know me, Philip? He who has seen me has seen the Father; how can you say, “Show us the Father”?’” (Jn 14:9).

Love

So, the Son is the Father’s Word, and a human word can serve as an analogy for understanding something of the Son’s personality. What is the Holy Spirit’s principal characteristic? CCC no. 221 notes the Holy Spirit’s personality as Love:

But St. John goes even further when he affirms that “God is love” (1 Jn 4:8): God’s very being is love. By sending his only Son and the Spirit of Love in the fullness of time, God has revealed his innermost secret: God himself is an eternal exchange of love, Father, Son and Holy Spirit, and he has destined us to share in that exchange.

We saw just above that in the act of knowing, the intellect produces a likeness of the object known. In the act of willing, what does the will produce? The known is in the knower by way of likeness, but how is the beloved in the lover? Aquinas explains that it is by way of inclination toward the thing willed. The will does not produce a likeness but an impulse toward the beloved. Thus, whereas the Son is the Word proceeding by way of birth as a likeness, the Holy Spirit is Love proceeding by way of spiration as an impulse. “Spiration” is taken from the Latin spiratio, which means “breathing.” The Father and the Son spirate, or breathe forth, the Holy Spirit.

Thus, as the Father’s act of knowing is so perfectly and truly productive that the likeness produced is another self within God, so the Father and the Son’s act of loving is so perfectly and truly productive that the impulse produced is so real, rich, and definitive that the image is a whole other living existing self who possesses the divine essence. As was the case with the Son, the impulse cannot be another divine essence, for there can only be one truly infinite divine essence. The only distinction between (the Father and the Son as) the Spirator and the Spirit is that the Father and Son breathe the Spirit forth and the Spirit is breathed forth. 

Thus, the Holy Spirit is not the Father or the Son, because He proceeds from the Father and the Son; and he proceeds from the Father and the Son by way of impulse—as an impulse of love in the will. And the love is so full and perfect that the Holy Spirit is no less than the Father and the Son. So, this analogy gives us real distinction between divine persons, perfect equality of essence, and an understanding of the Holy Spirit’s personality as Love, the bond of love between the Father and the Son. Furthermore, Aquinas appeals to the analogy of the word and love to show how the Holy Spirit proceeds from the Son. Namely, knowledge gives rise to love; we cannot love what we do not know. So, in God, Love proceeds from the Word: the Spirit proceeds from the Son. 

We can therefore understand the Son’s personality as being the perfect Image of the Father and the Holy Spirit’s personality as being a driving impulse of Love that unites the Father and the Son. We capitalize the name “Love” here for the same reason that we capitalize “Word”: they are proper names of divine persons as are Son and Holy Spirit.

CCC no. 221, quoted above, points out two perspectives on God as love. We have already considered the personal perspective above: The Holy Spirit is Love; that is, He is Love proceeding in the divine will—a person whose personality is Love. The first line of CCC no. 221 points to the essential perspective: “John . . . affirms that ‘God is love’ (1 Jn 4:16): God’s very being is love.” That is, God is essentially love; He is not love in any limited or defined way. God is the essence, definition, and infinite perfection of love; and God is the source of all other love. The same may be said of all pure perfections, that is, perfections that do not necessarily include creaturely limitation, such as having matter. Unlike the pure perfections of being and truth, having a body is a perfection that is necessarily material and thus limited. God is simply infinite subsisting being, truth, power, wisdom, love, and the like. So, God is essentially power, wisdom, and love. Each of the divine persons is infinite divine power, infinite divine wisdom, and infinite divine love. Nevertheless, only one person proceeds by way of wisdom (the Son) and only one person proceeds by way of love (the Holy Spirit). The Father, the Son, and the Holy Spirit are love essentially, but the only the Holy Spirit is Love personally.

V. The Father and the Son

Since fatherhood is a sheer perfection (i.e., it is not necessarily bound up with creaturely imperfection), it applies to God first of all and to creatures by analogy. So, the exemplar of fatherhood is God the Father with respect to God the Son. Creaturely fathers are analogously fathers with respect to their sons and daughters. And more distantly, God can be considered the Father of all creatures analogously. And here there are two possibilities: we can speak of the whole Trinity as the Father of creatures, or we can address the person of the Father as our Father on account of having been adopted in Baptism and taught by Christ to call his Father our Father.

By nature, all creatures are sons of the whole Trinity in an analogous sense. All three divine persons have a paternal relation to creatures because the act of creation is not proper to any of the divine persons but is common to all three: the whole Trinity is the uncreated principle of all creatures. If any divine person did not create, He would not be divine since God has in fact created. 

On the supernatural level, baptized humans are invited by Jesus to pray to his Father. Here, Christians are participating in the sonship of the only-begotten Son with respect to the person of the Father. It is true that by virtue of the Incarnation we call the Son “our brother” and His Father “our Father.” However, while being our brother is proper to the incarnate Son, being our Father is not proper to God the Father but is common to the Trinity.

The Catechism mentions two of these senses of divine paternity. First, CCC no. 239 considers “Father” as applied to the whole Trinity with respect to creatures:

By calling God “Father,” the language of faith indicates two main things: that God is the first origin of everything and transcendent authority; and that he is at the same time goodness and loving care for all his children. God’s parental tenderness can also be expressed by the image of motherhood, which emphasizes God’s immanence, the intimacy between Creator and creature. The language of faith thus draws on the human experience of parents, who are in a way the first representatives of God for man. But this experience also tells us that human parents are fallible and can disfigure the face of fatherhood and motherhood. We ought therefore to recall that God transcends the human distinction between the sexes. He is neither man nor woman: he is God. He also transcends human fatherhood and motherhood, although he is their origin and standard: no one is father as God is Father.

God is the source of all perfections, including maternal perfections. But as pure spirit, God is of course without gender, which requires a body. And we should not let bad fathers tarnish the name of God the Father. Fatherhood belongs first of all to God and analogously to all other fathers.

A second sense of divine paternity, that of the Father’s relation to the Son, is discussed in CCC no. 240:

Jesus revealed that God is Father in an unheard-of sense: he is Father not only in being Creator; he is eternally Father in relation to his only Son, who is eternally Son only in relation to his Father: “No one knows the Son except the Father, and no one knows the Father except the Son and any one to whom the Son chooses to reveal him” (Mt 11:27).

This “unheard-of sense” is known to us only through divine revelation.

VI. The Son and the Holy Spirit

CCC no. 243 confirms the revelation of a third distinct person in God, who guides the Church into the truth:

Before his Passover, Jesus announced the sending of “another Paraclete” (Advocate), the Holy Spirit. At work since creation having previously “spoken through the prophets,” the Spirit will now be with and in the disciples, to teach them and guide them “into all the truth.” The Holy Spirit is thus revealed as another divine person with Jesus and the Father.

Four other paragraphs of the Catechism report on key dogmatic declarations on the Holy Spirit, namely, on teachings we have from Jesus concerning the Holy Spirit’s procession from the Father and the Son. The most important affirmation is that the Holy Spirit proceeds as equally God with the Father and the Son:

The apostolic faith concerning the Spirit was confessed by the second ecumenical council at Constantinople (381): “We believe in the Holy Spirit, the Lord and giver of life, who proceeds from the Father.” By this confession, the Church recognizes the Father as “the source and origin of the whole divinity.” But the eternal origin of the Spirit is not unconnected with the Son’s origin: “The Holy Spirit, the third person of the Trinity, is God, one and equal with the Father and the Son, of the same substance and also of the same nature. . . . Yet he is not called the Spirit of the Father alone . . . but the Spirit of both the Father and the Son.” The Creed of the Church from the Council of Constantinople confesses: “With the Father and the Son, he is worshipped and glorified.” (<em>CCC</em> no. 245)

When it is said in this paragraph that the Father is the “source and origin of the whole divinity”—an expression taken from St. Augustine—it does not mean that the Father is the source of himself. It means that the Father has no origin and is the origin of the Son and of the Spirit.

The next three paragraphs deal with a controversy over the Spirit’s procession from the Son:

The Latin tradition of the Creed confesses that the Spirit “proceeds from the Father <em>and the Son (filioque)</em>.” The Council of Florence in 1438 explains: “The Holy Spirit is eternally from the Father and Son; He has his nature and subsistence at once (<em>simul</em>) from the Father and the Son. He proceeds eternally from both as from one principle and through one spiration. . . . And, since the Father has through generation given to the only-begotten Son everything that belongs to the Father, except being Father, the Son has also eternally from the Father, from whom he is eternally born, that the Holy Spirit proceeds from the Son.” (<em>CCC</em> no. 246)

A critical principle is articulated here: the Son is everything that the Father is except the Father himself; the Son has everything that the Father has except fatherhood (Aquinas, Contra Errores Graecorum II, ch. 28). The Father has the act of spiration, i.e., of breathing the Holy Spirit forth. So, the Son too must have this action, because he has fully the same divine essence as the Father does. The Father and the Son are together one single Spirator of the Holy Spirit (Aquinas, ST I, q. 36, a. 4, ad 7). There is no “double procession” of the Holy Spirit. As the Father and the Son have one same divine essence, so are they one single perfectly united principle in breathing the Holy Spirit forth. 

Because of the controversy over the filioque, it is important to document significant points in the history of its use:

The affirmation of the <em>filioque</em> does not appear in the Creed confessed in 381 at Constantinople. But Pope St. Leo I, following an ancient Latin and Alexandrian tradition, had already confessed it dogmatically in 447, even before Rome, in 451 at the Council of Chalcedon, came to recognize and receive the Symbol of 381. The use of this formula in the Creed was gradually admitted into the Latin liturgy (between the eighth and eleventh centuries). The introduction of the filioque into the Niceno-Constantinopolitan Creed by the Latin liturgy constitutes moreover, even today, a point of disagreement with the Orthodox Churches. (<em>CCC</em> no. 247)

Unfortunately, in 867, Photius, the Patriarch of Constantinople, condemned the filioque as heretical. One could propose that the filioque not be included in the creed that is recited at Mass on Sundays in Constantinople, but a declaration that this teaching is heretical is in fact itself an act of heresy. If the Spirit does not proceed from the Son, then He cannot be distinct from the Son. The Father, the Son, and the Holy Spirit are one same God with one same intellect and will. They are not distinct in being, goodness, truth, perfection, or infinity. The only way that the divine persons are distinct is that one comes from another: the Son comes from the Father and the Spirit comes from the Father and the Son. There is no other way to distinguish the divine persons. Therefore, if the Spirit does not come from the Son, then He is the Son using an alias.

Now, “from” is not the only preposition that can be used to express how the Spirit is toward the Son; one may also say that the Spirit proceeds from the Father through the Son:

At the outset the Eastern tradition expresses the Father’s character as first origin of the Spirit. By confessing the Spirit as he “who proceeds from the Father,” it affirms that he <em>comes from</em> the Father <em>through</em> the Son. The Western tradition expresses first the consubstantial communion between Father and Son, by saying that the Spirit proceeds from the Father and the Son (<em>filioque</em>). It says this, “legitimately and with good reason,” for the eternal order of the divine persons in their consubstantial communion implies that the Father, as “the principle without principle,” is the first origin of the Spirit, but also that as Father of the only Son, he is, with the Son, the single principle from which the Holy Spirit proceeds. This legitimate complementarity, provided it does not become rigid, does not affect the identity of faith in the reality of the same mystery confessed. (<em>CCC</em> no. 248)

If you wish to emphasize the order of persons in the Trinity, i.e., that the Son is from the unoriginate Father, and the Spirit is from the Father and the Son, then you should say that the Holy Spirit proceeds from the Father through the Son. If you wish to emphasize the perfect unity of the Spirator, i.e., the Father and the Son as one single principle of the Spirit, then you should say that the Holy Spirit proceeds from the Father and the Son.

CCC no. 244 takes up the language of John 14:26, where we read that the Father will send the Spirit in Jesus’s name: “The Spirit is sent to the apostles and to the Church both by the Father in the name of the Son, and by the Son in person, once he had returned to the Father.” This should not be interpreted to mean that the Spirit can ever proceed from the Father alone without the Son also spirating the Spirit as one single principle with the Father. If the Son were impossibly ever not the principle of the Spirit, then He would never be the principle of the Spirit. These relations are eternal and unchanging. Again, if the Son were ever in any way not the principle of the Spirit, then He would simply be the Spirit sporting a new nickname.

VII. Relations in the Trinity

The concept of relation offers a concise and powerful way of speaking about personal distinction in the Trinity. St. Basil of Caesarea is the first to introduce the term “relation” (schesis) into the theological discussion; however, the idea is clearly suggested in Scripture in the revelation that there is a Son who comes from a Father. In combating heresies, the Church needed a way to articulate how the Father is not the Son or the Holy Spirit, and the Son is not the Holy Spirit, yet each person is the numerically same divine essence. If they are not distinct in essence, then how are they distinct? They are distinct by relation. Aquinas will make relation do the heavy lifting in his Trinitarian theology—in understanding a divine person as a subsistent relation, i.e., a relation that subsists as the divine essence.

What is a relation? It is a being-toward. It expresses how one thing stands with respect to another. Philosophers classify relation as an “accident.” The ancient Greek philosopher Aristotle identified ten categories according to which every material being can be comprehensively identified: substance plus nine kinds of properties, which he called accidents. These nine accidents are quantity, quality, action, passion, time, place, posture, habit, and relation. Relations relate a subject to a term based on one of these nine accidents—less relation. For example, a son (subject) is related to his mother (term) based on birth (action as the foundation); this relation is called sonship. A man (subject) can be twice as old (time as the foundation) as his dog (term); this relation is “older” or “twice as old.”

Among these ten categories, only in relations do we find something that can be only in our apprehension and not in the real order. That is, relations can be merely logical. How one thing stands toward another can be in the mind only and have no existence in reality. This is not found in any of the other eight accidents that describe being. All of the other accidents, according to their strict and proper meaning, signify something inhering in a subject. For instance, quantity must actually be in the substance; every material being must have a real age, such that time is really a property of that thing. And place must really describe a substance: the substance must be in some place in the real order. But relation, according to its proper meaning, signifies only what refers to another. Relation does not have to positively describe the subject, but only to order it to another. This gives relation an ecstatic character: it borrows its reality from some other thing. Because of this, among the ten categories, relation is the freest of the limits of the material subject and is in a sense the weakest of the nine accidents and the most distant from substance. Hence it is the best category we have to apply to distinction in the Trinity because we want something that can signify distinction without touching substance: the divine persons are distinct, but they are one same substance.

If a relation is only in our apprehension and has no foundation in the real order, then it is merely a logical relation. But if it has a foundation in reality, then it has accidental existence in the substance as the eight other accidents do. That means that a real relation has two aspects. It is in a substance, and thus it has being-in; and it relates the substance to another, and thus it has being-toward. Let us consider the example of real relations based on quantity. When we say that a two-foot snake is to a four-foot snake as half to double, that relation of half to double is based on a quantity that is really in the snakes, i.e., two feet long and four feet long. For that reason, we understand the relation itself to have accidental existence in the substance. The two-foot snake’s relation of being half as long as the four-foot snake is a real relation inhering in the snake; it is not merely a relation in the mind of the one comparing the snakes. The relation has being-in. 

Now, the relation also has being-toward. All relations have being-toward, otherwise they would not be relations because they would not be relating anything. The proper signification of a relation is being toward. That is, its only job is to say how one thing stands with respect to another. Even if it is a real relation, its signification only concerns how one thing is related to another thing. So, to return to our example, the two-foot snake is toward the four-foot snake as half in length. Because relations signify being toward something else, they come in pairs—opposed pairs. For instance, the two-foot snake is only half in length with respect to something else that is four feet long; we cannot say simply that it is half as long, without reference to anything else. 

In considering relations in the Trinity, Aquinas will align the aspect of being-in with the divine essence or unity of the persons; and he will align the aspect of being-toward with the persons in their distinction. In this way, there is not identical unity on one side and real distinction on the other, but one and three converge in the relation. Now, of course, there are no accidents in God; so relation does not inhere in God like some property inhering in a substance. Whatever is in God is simply God (Aquinas, ST I, q. 27, a. 3, ad 2), and thus each relation is the same as the divine essence in the real order. That is why Aquinas aligns the divine relation’s being-in with the divine essence. This gives us Aquinas’s famous doctrine of subsistent relations. Each divine relation, which is a being-toward according to its signification, subsists in the real order as the divine essence. It is a being-toward made of the divine essence (taking “made” without any sense of being created). In discussing the mystery of the Trinity, one challenge has always been to knit identity of essence together with real personal distinction, and not just talk about one and then the other. Here Aquinas has found a conceptually brilliant way to do so. We are in no way pretending to resolve the mystery, but only to lay hold of it insofar as possible with our limited intellects.

So, how can the Father, the Son, and the Holy Spirit be said to be distinct if they are each one numerically same divine essence? CCC no. 255 gives us the answer: the divine persons are distinct relatively—or by relation:

<em>The divine persons are relative to one another.</em> Because it does not divide the divine unity, the real distinction of the persons from one another resides solely in the relationships which relate them to one another: “In the relational names of the persons the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance.” Indeed “everything (in them) is one where there is no opposition of relationship.” “Because of that unity the Father is wholly in the Son and wholly in the Holy Spirit; the Son is wholly in the Father and wholly in the Holy Spirit; the Holy Spirit is wholly in the Father and wholly in the Son.” (<em>CCC</em> no. 255, emphasis in original)

With this understanding, we can explain better how to interpret the idea that “the divine Unity is Triune,” as asserted in CCC no. 254 above. This must be interpreted to mean that the perfectly indivisible unique divine essence is possessed by three persons. It does not mean that the essence itself is somehow marked with perforated lines into three parts. There is absolutely no basis of distinction in the Trinity other than relative opposition; and relative opposition is completely absent from the divine essence as such. Also, there can be no parts in God, which would be suggested if there were real distinction within the essence itself. And furthermore, if the essence itself were somehow three, we should be able to discern that (albeit faintly) by reason alone through God’s effects.

We must resist the temptation to build plurality into the essence itself to make this mystery conceptually easier. We must live with the tension of the mystery. That is best achieved by having our language reflect that tension. 

In his doctrine of subsistent relations, Aquinas makes a subtle rhetorical move. As we established above, a divine relation is the divine essence in the real order. This is not enough theological work, however, for a discussion about the essential equality and personal distinction in the Trinity. We must also talk about persons who are revealed in Scripture. A relation is a being-toward. It does not signify the perfection of being something. However, “person” does signify the perfection of being something. So, in Aquinas’s view, the divine person is a divine relation now taken as signified according to substance, so that it is a who, not a being-toward. In other words, the divine person is a relation insofar as that relation subsists as the divine essence. This is an elaborate construction, but it makes a decisive advance in securing the “both/and” of the mystery. The Father is divine paternity insofar as divine paternity subsists as the divine essence. In other words, the Father is the divine essence as towards the Son; the Son is the divine essence as towards the Father; and the Spirit is the divine essence as towards the Father and the Son.

VIII. The Missions of the Divine Persons

The divine missions refer to the sending of the Son and the Holy Spirit into the world to save us. The Father is not sent, because He is unoriginate; He does not proceed from anyone; thus, he has no one to send him. As noted above, there are visible and invisible missions. Regarding the visible missions, whereas Christ’s human nature is personally united to God the Son, the visible missions of the Spirit are only signs that manifest the invisible presence of the Spirit in grace.

The invisible missions of the Son and the Holy Spirit are the indwelling of the Son and the Holy Spirit in the soul through grace. The Father dwells in the soul through grace, but He is not sent. CCC no. 257 observes that God’s plan from all eternity unfolds in the divine missions:

“O blessed light, O Trinity and first Unity!” God is eternal blessedness, undying life, unfading light. God is love: Father, Son and Holy Spirit. God freely wills to communicate the glory of his blessed life. Such is the “plan of his loving kindness,” conceived by the Father before the foundation of the world, in his beloved Son: “He destined us in love to be his sons” (Eph 1:4-5, 9) and “to be conformed to the image of his Son,” through “the spirit of sonship” (Rom 8:15, 29). This plan is a “grace [which] was given to us in Christ Jesus before the ages began” (2 Tm 1:9-10), stemming immediately from Trinitarian love. It unfolds in the work of creation, the whole history of salvation after the fall, and the missions of the Son and the Spirit, which are continued in the mission of the Church.

So, the whole Trinity dwells in the soul and its powers (the intellect and will) by sanctifying grace, and grace conforms the soul to God. Aquinas explains that in knowing and loving God with the assistance of grace, we become a miniature image of the Trinity. The Trinity is to be understood as God knowing and loving Himself, as we described in the analogy of the word and love above. In God’s knowing and loving Himself, the Father produces the Word, and the Father and the Son produce the Holy Spirit. In the invisible missions, the soul is likened to the persons sent, who then dwell in the soul. In this way, the soul is assimilated to the Son by the gift of wisdom and to the Holy Spirit by the gift of charity. That is, the Son proceeds as the Word and wisdom of the Father, so the mission of the Son is by way of wisdom; and the Holy Spirit proceeds as the Love of the Father and the Son, so the mission of the Holy Spirit is by way of charity. In a beautiful line, Aquinas writes that “the Son is not just any Word, but one that breathes forth Love.” That is, “The Son is sent not in accordance with every and any kind of intellectual perfection, but according to the intellectual illumination that breaks forth into the affection of love” (ST I, q. 43, a. 5, ad 2). This intellectual illumination is not mere discursive reasoning.

Because of this indwelling, it is possible for us in a certain way to experience the proper relations of the divine persons since the gifts of grace refer us to the divine persons in their distinctiveness: wisdom gives us a share in the way that the Son is related to the Father, and charity gives us a share in the way that the Holy Spirit is related to the Father and the Son. Aquinas elaborates on this in I Sent., d. 15, q. 4, a. 1, corp.:

This procession of a divine person [leading rational creatures back to God] is called a mission insofar as the proper relation of the divine person himself is represented in the soul through a received likeness that is patterned on and originated from the property itself of the eternal relation . . . . And because according to the reception of these two, a likeness to the properties of the persons is effected in us, therefore according to a new mode of being, as a thing is in its likeness, the divine persons are said to be in us insofar as we are assimilated to them by this new mode.

The Son and the Holy Spirit are in us insofar as we are assimilated to them through our sharing in their personal properties. Our filiation with respect to the Father is mediated and accomplished by likenesses in us of the Son’s and the Holy Spirit’s proper relations to the Father. But how is it possible for a creature to have a distinct relation to just one person of the Trinity, since every action in the created order is performed by all three persons acting as a single principle? All three persons must be acting in every action in the created order because if any one of them were not, then He would not be God—since God would be acting and yet this person would not be. The Catechism provides the beginning of an explanation, pointing to the missions as the clearest example of a distinct relation to just one divine person:

The whole divine economy is the common work of the three divine persons. For as the Trinity has only one and the same nature, so too does it have only one and the same operation: “The Father, the Son and the Holy Spirit are not three principles of creation but one principle.” However, each divine person performs the common work according to his unique personal property. Thus the Church confesses, following the New Testament, “one God and Father from whom all things are, and one Lord Jesus Christ, through whom all things are, and one Holy Spirit in whom all things are.” It is above all the divine missions of the Son’s Incarnation and the gift of the Holy Spirit that show forth the properties of the divine persons. (<em>CCC</em> no. 258)

Distinct Personal Modes of Action

A key principle articulated in CCC no. 258 just above is that the divine persons do not lose their personality just because they act as a single principle in the created order. They act together as a single principle but the Father as the Father, the Son as the Son, and the Spirit as the Spirit. That is, the Father acts as the one who has no principle but speaks the Word and breathes forth the Spirit; the Son acts as the Word proceeding from the Father, breathing forth the Spirit; and the Spirit acts as the Love breathed forth by the Father and the Son. So, although no creature has the density of being sufficient to manifest this distinction of persons (so that by examining created effects, reason alone cannot deduce the existence of the Trinity) each divine person still acts according to His distinct personality. That is why we can say that the Father creates through the Son and the Holy Spirit, as proclaimed in CCC nos. 291 and 292:

“In the beginning was the Word. . . and the Word was God. . . all things were made through him, and without him was not anything made that was made.” The New Testament reveals that God created everything by the eternal Word, his beloved Son. In him “all things were created, in heaven and on earth . . . all things were created through him and for him. He is before all things, and in him all things hold together.” The Church’s faith likewise confesses the creative action of the Holy Spirit, the “giver of life,” “the Creator Spirit” (<em>Veni, Creator Spiritus</em>), the “source of every good.”

The Old Testament suggests and the New Covenant reveals the creative action of the Son and the Spirit, inseparably one with that of the Father. This creative cooperation is clearly affirmed in the Church’s rule of faith: “There exists but one God. . . he is the Father, God, the Creator, the author, the giver of order. He made all things by himself, that is, by his Word and by his Wisdom,” “by the Son and the Spirit” who, so to speak, are “his hands.” Creation is the common work of the Holy Trinity.

This teaching shows that divine revelation gives us insight into the created order that reason alone could never gain. For instance, in the divine missions, the gifts of knowledge and love lead us to the whole Trinity, because the whole Trinity causes these effects in us according to efficient causality, as we noted just above. However, according to exemplar causality, the gift of knowledge has a proper real relation to the Son, and the gift of love has a proper real relation to the Holy Spirit. When the creature, made in the image of God as a knower and a lover, has these two powers of knowing and loving elevated by grace so that he can have God as the object of these powers, then the gifts of knowledge and love assimilate this rational creature to the Son and the Holy Spirit, respectively. By his exercise of the gift of wisdom (which perfects the intellect), man is assimilated to the Son and shares in the Son’s relation to the Father, and by his exercise of the gift of charity (which perfects the will), man is assimilated to the Holy Spirit and shares in the Holy Spirit’s relation to the Father and the Son.

There is a subtle balance here. All divine actions in the created order are necessarily the work of all three persons of the Trinity (through efficient causality), but in the invisible missions of the Son and the Holy Spirit, the effects in the created order have just one divine person as their exemplar (through exemplar causality). The mission of the divine person is brought about by an effect that is a likeness of the property of that divine person and not any other person.

With this understanding, we can now make sense of CCC no. 259:

Being a work at once common and personal, the whole divine economy makes known both what is proper to the divine persons, and their one divine nature. Hence the whole Christian life is a communion with each of the divine persons, without in any way separating them. Everyone who glorifies the Father does so through the Son in the Holy Spirit; everyone who follows Christ does so because the Father draws him and the Spirit moves him (See Jn 6:44 and Rom 8:14).

How is the created order a work both common and personal? All three persons act as a single principle, but each person acts according to His distinct personality. How are the divine persons and the divine nature made known in the created order? Something of God’s nature can be known by reason alone, such as His goodness, omnipotence, and eternity. But through revelation, we have a confirmation of what can be known by reason alone, and we are also given knowledge of God as He is in Himself—as the Trinity. And with this revelation, we can then see in the created order effects that point us back to a single divine person. This happens above all through the missions, as CCC no. 258 observed, but it is not only through the missions. It happens also through “appropriation,” which we will discuss shortly below.

To complete our treatment of the divine missions, we should point out that there is no likeness of a property of the Father produced in the soul by grace. The Father gives Himself in grace, but He is not sent since He is without origin (ST I, q. 43, aa. 4-5). Instead of being conformed to the Father by a likeness of Him in the soul, we are referred back to the Father as our ultimate end by sharing in the proper relations that the Son and Holy Spirit have to the Father, who lead us back to and join us to Him. This is how we should interpret CCC no. 260:

The ultimate end of the whole divine economy is the entry of God’s creatures into the perfect unity of the Blessed Trinity (see Jn 17:21-23). But even now we are called to be a dwelling for the Most Holy Trinity: “If a man loves me,” says the Lord, “he will keep my word, and my Father will love him, and we will come to him, and make our home with him” (Jn 14:23).

IX. Appropriation

CCC no. 278 draws our attention to the doctrine of appropriation: “If we do not believe that God’s love is almighty, how can we believe that the Father could create us, the Son redeem us and the Holy Spirit sanctify us?” Now, as noted above, all three persons produce any effect in the created order. Therefore, the Father, the Son, and the Holy Spirit create, and all three also redeem and sanctify. How then can this paragraph of the Catechism associate creation with the Father, redemption with the Son, and sanctification with the Spirit? Is there any way in which it is acceptable to speak of the Trinity as the Creator, Redeemer, and Sanctifier? This association can be made by appropriation. 

In appropriation, we attribute common attributes or divine actions in the created order to individual divine persons. We do so in order to learn about the divine persons. By reason of a real affinity between an essential attribute (or action in the created order) and one of the divine persons, we can “appropriate” that essential attribute (or action) to that person. In appropriation, we appropriate something common to all three persons to one individual person, based on a likeness between the common attribute or action and a property of that person. In this way, we move from what is more known to what is less known in order to gain insight into the properties of the divine persons. Why is what is common more known to us than what is proper? Common attributes and divine actions are better known to us because they can be known by reason alone through created things, which, as God’s effects, reveal something about Him.

As an illustration, by knowing something about power, wisdom, and love, we can come to a deeper understanding of the Father, the Son, and the Holy Spirit, even though all three persons are equally infinite power, wisdom, and love. Power is the principle of action, and the Father is most a principle in the Trinity since two persons proceed from Him, and He does not proceed from anyone. Wisdom is the manner in which the Word proceeds from the Father, since He proceeds by way of intellect. Hence essential wisdom, which is common to all three divine persons, elucidates the Son, who is begotten Wisdom. And similarly, because the Spirit proceeds as an impulse of love in the divine will, essential love elucidates the Holy Spirit, who is the bond of love between the Father and the Son.

X. Knowledge of the Trinity as Necessary for Salvation

Aquinas affirms that, in order to be saved, we must know the Trinity: “The mystery of Christ cannot be believed in explicitly without faith in the Trinity, because included in the mystery of Christ is the fact that the Son of God assumed flesh, that he renewed the world through the grace of the Holy Spirit, and again, that he was conceived by the Holy Spirit” (ST II-II, q. 2, a. 8).

And Aquinas offers two reasons why knowledge of the divine persons was necessary for us: for the right idea of creation, and chiefly, for the right idea of salvation (ST I, q. 32, a. 1, ad 3). The point about the right idea of creation is addressed in the Catechism, which explains the significance of creation through the Son:

We believe that God created the world according to his wisdom. It is not the product of any necessity whatever, nor of blind fate or chance. We believe that it proceeds from God’s free will; he wanted to make his creatures share in his being, wisdom and goodness: “For you created all things, and by your will they existed and were created.” Therefore the Psalmist exclaims: “O LORD, how manifold are your works! In wisdom you have made them all”; and “The LORD is good to all, and his compassion is over all that he has made” (<em>CCC</em> no. 295).

Since God made all things by his Word, he made them freely and not by necessity; for whatever we produce through the concept of our intellect, we do freely. This rules out the error of those who say that God produced creatures by necessity.

And then CCC no. 293 explains the significance of creation through the Spirit:

Scripture and Tradition never cease to teach and celebrate this fundamental truth: “The world was made for the glory of God.” St. Bonaventure explains that God created all things “not to increase his glory, but to show it forth and to communicate it,” for God has no other reason for creating than his love and goodness: “Creatures came into existence when the key of love opened his hand.” The First Vatican Council explains: 

This one, true God, of his own goodness and “almighty power,” not for increasing his own beatitude, nor for attaining his perfection, but in order to manifest this perfection through the benefits which he bestows on creatures, with absolute freedom of counsel “and from the beginning of time, made out of nothing both orders of creatures, the spiritual and the corporeal. . . .”

Since God made creatures in an act of love, He made them not because He needed them, nor for any other extrinsic reason, but on account of the love of His own goodness. According to Aquinas, when God created heaven and earth, He said, “Let there be light,” to manifest the divine Word; and Genesis records that “God saw the light, that it was good,” to show proof of the divine love. So, God created freely and generously. 

Regarding the right idea of salvation, our redemption is accomplished by the incarnate Son and by the gift of the Holy Spirit. Without the revelation of the Trinity, we would have had no knowledge of the manner in which we are to be reconciled with and drawn back to the Father. With this revelation, we can make a free act of faith and be moved supernaturally by God to participate in our own salvation (ST I, q. 32, a. 1, ad 3). 

Turning to the Fourth Lateran Council for the relevant creedal formulation, CCC no. 202 notes the distinctive character of professing God as a Trinity:

Jesus gives us to understand that he himself is “the Lord.” To confess that Jesus is Lord is distinctive of Christian faith. This is not contrary to belief in the One God. Nor does believing in the Holy Spirit as “Lord and giver of life” introduce any division into the One God: “We firmly believe and confess without reservation that there is only one true God, eternal infinite (<em>immensus</em>) and unchangeable, incomprehensible, almighty and ineffable, the Father and the Son and the Holy Spirit; three persons indeed, but one essence, substance or nature entirely simple.”

Now, does that mean that those who did not hear the Trinity preached to them by the Christians cannot be saved? No. Before Christ’s coming, God gave implicit faith in Christ and the Trinity to individuals and to the whole nation of Israel. And after Christ’s coming, God gives implicit faith in Christ and the Trinity to individuals who through no fault of their own have not heard and accepted the doctrine preached by the Catholic Church. 

This idea does not spring from sentimental universalism. With respect to the justification of individuals, Aquinas teaches that an unbaptized person who deliberates about himself and his aim in life, and chooses the right goal, will have original sin forgiven and will receive grace (ST I-II, q. 89, a. 6). And with respect to Israel, Aquinas affirms that original sin was remitted in circumcision and grace was bestowed (ST III, q. 70, a. 4). Now, whereas baptism is the sign that effects the forgiveness of sins and the bestowal of grace, circumcision is merely a sign of the faith that justifies; circumcision is not the cause of the remission of sin and bestowal of grace. Baptism is an instrumental cause of grace; circumcision is not.

Furthermore, in Singulari Quadam Pius IX declared that invincible ignorance of the true religion is not a sin. And Vatican II teaches definitively that those who are ignorant of the Gospel through no fault of their own can be saved if they sincerely seek God and strive to do His will according to their consciences: God does not deny them the assistance of grace necessary for salvation (Lumen Gentium 16).

XI. The Real Effect of this Doctrine on our Lives

CCC no. 256 treats us to the inspiring words of the great Cappadocian Father St. Gregory of Nazianzus. In theology, so many words are necessary to make so many distinctions in defense of the faith because we think in propositions. But faith in Jesus and the Trinity is not ultimately about propositions. It is about being saved from death by the forgiveness of our sins. And this revelation has literally cost many Christians their lives. Jesus warned us, “If the world hates you, know that it has hated me before it hated you” (Jn 15:18). So, proclaiming the truth about the Trinity can bring a Christian into conflict with the world:

St. Gregory of Nazianzus, also called “the Theologian,” entrusts this summary of Trinitarian faith to the catechumens of Constantinople:

Above all guard for me this great deposit of faith for which I live and fight, which I want to take with me as a companion, and which makes me bear all evils and despise all pleasures: I mean the profession of faith in the Father and the Son and the Holy Spirit. I entrust it to you today. By it I am soon going to plunge you into water and raise you up from it. I give it to you as the companion and patron of your whole life. I give you but one divinity and power, existing one in three, and containing the three in a distinct way. Divinity without disparity of substance or nature, without superior degree that raises up or inferior degree that casts down . . . the infinite co-naturality of three infinites. Each person considered in himself is entirely God . . . the three considered together. . . . I have not even begun to think of unity when the Trinity bathes me in its splendor. I have not even begun to think of the Trinity when unity grasps me. . . .

Why God would raise us into being and call us to participate in his glory for all eternity remains a mystery to us—indeed, a terrifying mystery when we reflect on the depth of God’s mercy and the possibility of our falling away from our vocation permanently. We must know about the Trinity, and we must love the Trinity in order to be saved. For that reason, we have made the effort to produce this article, subdivided into eleven sections, with special attention to the Catechism of the Catholic Church and a foundation in the theology of St. Thomas Aquinas.