1. The Church teaches that there is one true God, Father, Son, and Holy Spirit, one in being but three in persons.3 The Father is not begotten; the Son is begotten of the Father; the Holy Spirit proceeds from the Father and the Son. None of the persons is identical with either of the others. The three persons are one God, not three gods; for they are one divine reality, a single entity, not three entities. There is multiplicity only in what is distinguished by the opposition of personal relationships: for example, of Father and Son to each other. Because of their unity, each person is wholly in each of the others. The Father, the Son, and the Spirit are not three principles of creatures, but one principle—one creator (see DS 1331/704).
2. Since we must understand God as a unity of three distinct persons, we can think of him, as the terms “Father” and “Son” require, as being familial. As familial, the divine persons are most perfectly united and most perfectly distinct. The ideal of love, in which unity and multiplicity are both at their ultimate, is best realized here; or, better, our ideal of love comes from this divine exemplar, proceeding from “the Father, from whom every family in heaven and on earth is named” (Eph 3.14–15).
3. Inculcating brotherly love, the First Epistle of John makes the point: “He who does not love does not know God; for God is love” (1 Jn 4.8). While the context indicates that the sacred writer is thinking of God’s love manifested in the Incarnation and redemptive act of the Son, still it seems warranted also to take the verse as an expression of the reality of the Holy Trinity which is truly revealed in Jesus.
Ceslaus Spicq, O.P., in summarizing his analysis of many Johannine texts, particularly those bearing upon the love of Father and Son, says:
There is so complete an identity between Christ’s love and the Father’s love that we can conclude from one to the other. It is more than a matter of manifestations and marks of love, as if God and Jesus were acting with one and the same heart. The relationship between the Father and his only Son springs from a reciprocal, permanent, and eternal charity (Jn 17.23–24). Everything that Christ has revealed about the intimate life of God is summarized in its being an exchange made within the mutual relationship of knowledge and love between God and his Son. The union of the two persons seems to be accomplished in agape [note: Jn 17.22-23, 26]. Thus one arrives at conceiving of a substantial charity which is God (1 Jn 4.10). Love is of the same nature as God.4
What is said here of the Father and the Son surely must be extrapolated to include the Holy Spirit. The inner reality of the Holy Trinity, it seems clear, is a communion which is infinite love (cf. S.t., 1, q. 37, a. 1).
4. The mystery of the Holy Trinity is a mystery of love. More specifically, it is a mystery of the communicability of divinity. That there are three divine persons in the one only God shows that divinity is not a monad—a self-enclosed absolute unit, which could neither be many without exploding into an infinity of particles nor gather the many into itself without absorbing them into an indistinguishable whole. God is not so. He is one in three, three in one. He is love, the perfect exemplar of love, the absolute reconciliation of the one and the many. This reconciliation is what philosophy always seeks and never finds; it is what sinful created persons always long for and never enjoy—until the Word becomes flesh and makes enduring love present in the world.
5. This has practical implications. Since God’s very constitution is love, sharing in his love is sharing in his life.
Every Christian doctrine has a normative aspect. God’s revelation demands a response from us, and everything God reveals should help to shape our response. In many cases, reflection has not made clear the practical significance of the most basic truths of faith, although their significance has been communicated more or less effectively to unreflective understanding by other means, especially by the words and deeds of the liturgy. The present chapter clarifies the practical significance of one of the most central doctrines of Christian faith, namely, the teaching on the Holy Trinity.
6. Non-Christians who think of God as absolutely and noncommunally one tend to suppose that the human relationship with God must take either of two forms: Either human beings must always remain extrinsic to God or they must be absorbed into him. The first possibility is reflected in Aristotle’s thought, the second in some Eastern thought.
7. Although God established a personal relationship with Israel, it lacked the intimacy of Christian communion with God in the Lord Jesus (21‑D). The sacramental communion of the old covenant was a meal which God deigned to permit in his sight (see Ex 24.11). The communion of the new covenant is a meal in which God not only takes part but gives himself (see Mt 26.26–29; Jn 6.53–58).
8. In sum, God is not a solitary being, nor an impersonal ocean of divinity. The Trinity, the one only God, is a communion of persons eternally one in love. Although apprehended only by the indirect light of faith, this mystery shows that divine life is not in principle incommunicable and that it is not necessarily communicated at the price of the dissolution of selfhood. A divine Father who has a natural Son is a God who can extend his family by adoption.5
Furthermore, the divine exemplar of love is a model for our brotherly and sisterly love. Teaching the importance of love of neighbor, Vatican II explains: “Indeed, the Lord Jesus, when he prayed to the Father, ‘that all may be one . . . as we are one’ (Jn 17.21–22) opened up vistas closed to human reason. For he implied a certain likeness between the union of the divine persons, and the union of God’s sons in truth and charity. This likeness reveals that man, who is the only creature on earth which God willed for itself, cannot fully find himself except through a sincere gift of himself” (GS 24). The divine family of the Trinity is the model for the human family called to become the extended family of God.
Love always involves a gift and depends upon initiative. Someone must make the first move. Often, who does so is dictated by who can do so—for example, parents love their children into being. Analogously, in the life of God, the Father has the initiative in begetting the Son, and the Father and Son have the initiative in breathing forth the Spirit. By free choice, God has the initiative in creating the world. The Incarnate Word has the initiative in redeeming the fallen world.
Initiative establishes priority—of course, one must realize that initiative and priority are diverse within God from his initiative and priority toward creatures. But if one bears in mind the analogous sense of the statement, one can say that love always establishes order, and the order once established is never lost. The basic priority is built into the interpersonal relationship; to deny it or to try to reverse it is to negate what the relationship really is.
Among the persons of the Trinity, the priority apparently holds in the salvific and sanctifying missions of the Son and Holy Spirit: “The words that I say to you I do not speak on my own authority; but the Father who dwells in me does his works” (Jn 14.10). The Holy Spirit “. . . will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak” (Jn 16.13).
Such priority clearly does not mean that the Father is superior and the Son inferior. The Holy Spirit is not deprived of freedom in teaching because he does not speak on his own. Something similar is manifested in Jesus’ washing of his disciples’ feet (see Jn 13.12–16) and his subsequent remarks about their status as friends rather than slaves (see Jn 15.14–15). Of course, love does not eliminate real differences. But neither does the order which love necessarily implies entail that the one who has initiative is in a higher caste than the one who first receives.
One concrete example illustrates the tremendous significance of this point. St. Paul teaches: “Wives, be subject to your husbands, as to the Lord” (Eph 5.22). This teaching does not consign Christian wives to an inferior position. In the marital relationship, the husband has priority in giving, based upon the actual dynamics of the psychobiology of sex. In the maternal-filial relationship, as Paul remarks elsewhere, women have priority to men (see 1 Cor 11.12). The consequence of the priority of the husband in giving to his wife is that he must sacrifice himself for her: promote her security and fulfillment, not his own comfort, success, and pleasure (see Eph 5.25). For her part, a wife cannot proceed autonomously, as though she did not need her husband. The abuse of the male role is to dominate and exploit, to use one’s wife for one’s own ends. The abuse with which wives respond to this exploitation is refusal to submit: an irresponsible declaration of liberty.6
3. A basic introduction to Catholic doctrine on the Trinity: Ronald Lawler, O.F.M.Cap., Donald W. Wuerl, and Thomas Comerford Lawler, eds., The Teaching of Christ: A Catholic Catechism for Adults (Huntington, Ind.: Our Sunday Visitor, 1976), 174–85; a fuller treatment: E. J. Fortman, The Triune God (Philadelphia: Westminster Press, 1972).
4. Ceslaus Spicq, O.P., Agape in the New Testament, vol. 3, Agape in the Gospel, Epistles and Apocalypse of St. John (St. Louis: B. Herder, 1966), 166. Also see Matthew Vellanickal, The Divine Sonship of Christians in the Johannine Writings, Analecta Biblica, 72 (Rome: Biblical Institute Press, 1977), 302–16; Raymond E. Brown, S.S., The Epistles of John, Anchor Bible, 30 (Garden City, N.Y.: Doubleday, 1982), 194–95, 515, 549–53.
5. See Matthias Joseph Scheeben, The Mysteries of Christianity (St. Louis: B. Herder, 1946), 141–48. Note the assertion (142): “Not God’s creative power, but His generative power enables us to apprehend that the generation of adoptive children is possible.” Scheeben does not go so far as to say that Christians are transformed by receiving a share in the uncreated divine nature, but his analysis points in that direction, and what he says is helpful toward articulating the point of view taken in this chapter.
6. For a very helpful treatment of this point, see Stephen B. Clark, Man and Woman in Christ: An Examination of the Roles of Men and Women in Light of Scripture and the Social Sciences (Ann Arbor, Mich.: Servant Books, 1980), 39–45 and 72–87.