The Splendor Of The Three-In-One God: The Necessity And Mystery Of The Trinity (Part One)

by on November 21, 2025

“Hear, O Israel, the Lord our God, the Lord is one!” (Deut 6:4) In contrast to the polytheistic religions of her neighbors, Israel was made deeply conscious of the fact that there is only one God (hence, the term, monotheism). The monotheistic doctrine of God is at the headwaters of the Christian faith, but it is the doctrine of the Trinity which makes our doctrine of God distinctively Christian. Islam, one of the world’s fastest growing religions, is monotheistic, but rejects entirely the doctrine of the Trinity as unreasonable. Jewish critics have long regarded the doctrine of the Trinity as polytheistic. Clearly the doctrine of the Trinity is a stumbling block to vast numbers of people, but without it we are no longer Christians. The Trinity is among those doctrines by which heresy (as distinguished from error) against the “catholic, undoubted Christian faith” is properly judged (Heidelberg Catechism 22). Since the fourth century AD, the agreement among orthodox, catholic Christians on the essentials of the doctrine of the Trinity has greatly outdistanced agreement on many other doctrines (e.g., the doctrine of salvation).1

Given the centrality to our faith of our teaching about the Trinity, it is profoundly ironic that for most believers this doctrine is practically disposable. In my experience, most North American evangelical Christians when asked to state the doctrine of the Trinity (if they can do it at all) will almost always give a heretical answer. The most common heresy among Western Christians has been modalism, which is the notion that God is not really one God in three persons, but rather only appears to be three persons. This is what we often teach in our Sunday Schools by way of the illustrations we use which imply that God wears a series of masks (first Father, then Son, then Spirit) or takes different forms under different conditions (e.g., water in solid, liquid, and gas forms).2

The Christian view of God is, as the Athanasian Creed teaches, that:

We worship one God in Trinity, and Trinity in Unity; neither confounding the Persons, nor dividing the Substance. For there is one Person of the Father, another of the Son, and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one, the Glory equal, the Majesty co-eternal.

As this creed continues, “The Father is Almighty, the Son Almighty, and the Holy Ghost Almighty. And yet they are not three Almighties, but one Almighty.” In biblical, creedal, and Christian teaching, God is one substance (Deut 6:4). Whatever it is which makes the Father to be God, is that which makes the Son and the Spirit to be God: “Such as the Father is, such is the Son, and such is the Holy Ghost” (Athanasian Creed).

At the same time, tri-personality is also essential to the Deity: “For there is one Person of the Father, another of the Son, and another of the Holy Ghost” (Athanasian Creed). It is possible to conceive of a god who is unipersonal, but the history of theology shows that any such god would necessarily be impersonal and so transcendent as to be unknowable, which is practical atheism.3 If we lose God’s tri-personality we forfeit our Christology. We believe that Jesus Christ is God the Son in the flesh, that he is of the same substance as God the Father and God the Spirit. We would also forfeit our Pneumatology (that is, the doctrine of the Holy Spirit) since we also believe that God the Spirit is of the same substance as the Father and the Son. If this is so (and without these truths one cannot be a Christian!), then God must be triune. As the Athanasian Creed puts it: “Unity in Trinity and the Trinity in Unity is to be worshipped.”

How this can be is a mystery, but it is a necessary mystery. It is necessary because “we are compelled by the Christian verity” to confess this doctrine (Athanasian Creed). It is necessary because: “Whosoever will be saved, before all things it is necessary that he hold the catholic Faith. Which Faith except everyone do keep whole and undefiled, without doubt he shall perish everlastingly” (Athanasian Creed). It is a necessary doctrine because our very destiny is at stake, not merely fine points of doctrine.

The Necessity of the Trinity

The way one reads the Bible is intimately related to the God one finds revealed there. Christians, being Trinitarian, read the Bible as a unity. That is, because God is one, the Scriptures are one. If God is revealed to be triune in the New Testament, we should expect to find him so revealed in the Old Testament. God’s Word itself recommends this hermeneutic: 1 Peter 1:10-12 teaches us that the same Holy Spirit who inspired Moses and the prophets also inspired the apostles as they interpreted the law and the prophets for us.

It also means, as John 1:1 teaches us, that the Son has always been God’s Word. He did not become the Word only in the incarnation, but rather he was the Word “in the beginning.” More than that, he was “with” God the Father, which means that he has always been personally distinct from the Father. At the same time, the Word “is God,” which means that God the Son and God the Father are, as the Nicene Creed states, “of the same substance” (consubstantial). Thus, the apostle John teaches us not to read the Son into the Old Testament, but to refuse to read him out of it.

Hence, when we consider the fundamental Israelite confession about God, “Hear O Israel, Yahweh our God, Yahweh is one” (Deut 6:4), we understand that this unity not only permits but entails tri-personality. Indeed, read from the perspective of the New Testament—how else can a Christian read Scripture?—the Old Testament is rich with Trinitarian revelation. The New Testament turns to several places in the Old Testament for its doctrine of the Trinity. Psalm 110 is cited more than any other Old Testament passage (see Matt 22:44; 26:64; Mark 12:36; 14:62; Luke 20:42–43; 22:69; Acts 2:34–35; Heb 1:13; 5:6, 10; 7:17, 21). The psalm speaks of the accession and rule of a Davidic Priest-King. The New Testament, however, focuses consistently on the doctrinal teaching of the psalm and, therefore, regards it as a promise of the ascension and inter-adventual reign of Christ. In that case, the primary reference of the psalm is not (as Peter reminds us in Acts 2:34–35) to David, but to the intra-Trinitarian relations between the Father and the Son and the outworking of those relations in redemptive history.

A second strand of Trinitarian revelation in the Old Testament is the revelation of the Son in the history of redemption in the person of the Angel of the Lord (Malak Yahweh). When the Angel of the Lord appeared, he was treated not as a mere heavenly representative of God, but as God himself; he did not reject worship, but accepted it as only God can. (Typically it is only after one has had an encounter with the Angel of the Lord that one realizes that, in fact, it was no mere angel but God himself; see Gen 16:9–13; 22:11–18; 32:28–30; Exod 3:2–6; Judg 6:11–14, 22; 13:22.) Both Augustine and Calvin interpreted these manifestations as wonderfully cryptic revelations of God the Son in a pre-incarnate state.4

John 1:1–3 teaches that when Genesis 1:1 says, “In the beginning God created the heavens and the earth,” we should understand that creation occurred through the agency of God the Son and that his work was essential to the act of creation because the Creator God is triune.

The work of redemption was also a Trinitarian work. Think, for instance, of the deliverance of God’s people from Egypt. On the principle that the God who revealed himself to Israel is triune, and that the Son has always been the Word (God’s authoritative self-revelation), we should consider that it was God the Son who met Moses in the burning bush, and at the top of Mount Sinai: “No one has ever seen God; God the only begotten who is in the bosom of the Father, this one has revealed him” (John 1:18). Jesus declared, “Anyone who has seen me, has seen the Father” (John 14:9). The writer to the Hebrews teaches that Christ is not only the “radiance of the glory” but the “exact manifestation” of the “divine being” (hypostasis), “sustaining all things by his powerful word” (Heb 1:3).

Hebrews 12:18–24 contrasts Mount Sinai with that mountain to which we have come. In so doing, however, it also tells us how we should think about the God who revealed his “hindmost quarters” to Moses. The mountain to which Moses came was covered in darkness, fire, gloom, and storm. In the new covenant, believers have come, however, to thousands of angels, to “the church of the firstborn, whose names are written in heaven. You have come to God, the judge of all men, to the spirits of righteous men made perfect, to Jesus the mediator of a new covenant, and to the sprinkled blood that speaks a better word than the blood of Abel” (Heb 12:23–24). Notice how the writer to the Hebrews uses a series of parallel expressions to drive home the same point: “church of the firstborn” (i.e., the risen Christ), “God, the judge of all men” who is “Jesus the mediator of a better covenant.” It was the Son who was revealed awesomely at the top of Sinai, who met with the elders, before whom they ate and drank, whom they “saw and did not die” (Exod 24:9–11), and it is the Son with whom we have to do today.

There is significant evidence that God the Spirit was also active in creation. The New International Version is right to spell Spirit with the capital S in Genesis 1:2. The “Spirit of God was hovering over the waters.” That such work is proper to the Spirit is suggested in 1 Peter 4:14, which uses the same image to describe the Spirit’s relations to the new covenant temple people. By the analogy of Scripture, we understand that it was God the Spirit who guided us through the wilderness. The pillar of divine presence surrounds and protects God’s people, hovering over his creation and new creation, indwelling and sanctifying, as he ever has.5

God the Father was also active in creation, speaking the Word, present in the redemption of Israel in the person of the Son, by the power of the Spirit. Who else could have passed over Israel for the sake of the blood of the lamb, but God the Father? One has only to think of how the Father provided earthly manna for his people and how he gave that ultimate manna which gives eternal life to all who eat by faith (John 6:31–33). Certainly, one sees wonderful evidence of his providence throughout the Hebrew Scriptures. At each turn the Father was meeting our needs, with drink from the rock and food from heaven (Num 20:11, 1 Cor 10:1–4). All this establishes not only that God revealed personal distinctions in the Old Testament, but that he revealed himself as tri-personal.

The new covenant Scriptures make explicit what was implicit in the old covenant. We may begin with our Lord, himself a Trinitarian theologian. His conception of himself and of his relations to the Father and the Spirit was unreservedly Trinitarian. This is not surprising given that he was himself a member of the triune Godhead, God the co-eternal, eternally begotten Son incarnate. We have already reviewed Jesus’ revelation of the personal distinction between himself and the Father. He also made clear that God the Spirit has his proper work drawing sinners to the Son; “the Spirit blows where he will” and without the work of the Spirit no one is able to see the kingdom of God (John 3:8).

Christ’s Trinitarian consciousness is clearly evident in his command to baptize in the triune name of God. “Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” (Matt 28:19). Notice that Jesus said, “in the name.” This is a most significant expression in Scripture. Out of the burning bush God the Son revealed the divine name to Moses: I AM. God’s name is who he is in himself, and also who he is in relation to us, the self-existent one. Thus, Herman Bavinck was right to say that, in this passage, Jesus drew together all the Trinitarian revelation of God in Scripture.6

Paul was equally explicit about God’s tri-personality in the benediction contained in 2 Corinthians 13:14 in which he named each of the Trinitarian persons: “May the grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all.” (This expression is doubtless linked to the Aaronic benediction of Numbers 6:24–26.) This was Paul’s consistent language about God. Frequently he used the noun “God” to refer to the Father (e.g., Rom 1:1, 7, 8; 8:14–17; 15:5–6; 1 Cor 1:3; 8:6; 11:3; 2 Cor 1:2; Gal 1:3; Eph 1:2, 17; 4:6; 5:20). He refers to the Son as “Christ” and to the third triune person as the “Spirit.” Read this way, his epistles are replete with allusions to the Trinity.

It is no wonder then that the earliest Fathers of the Christian church developed the biblical Trinitarianism almost immediately. This teaching was crystallized in the great ecumenical creeds: The Apostles’ Creed, the Nicene Creed (325 AD), the Athanasian Creed (381–421 AD) and the Chalcedonian Definition (451 AD).7

Against the Arians, Athanasius (c. 293–373), an Alexandrian archdeacon, defended stoutly the doctrine of the eternal generation of the Son. When Scripture says “only begotten God,” it means that the Son has always been begotten of the Father (see John 1:18). There has never been a point (remember we are speaking of eternity) when the Son was not. The Son has always been the Son and the Father has always been his Father. This eternal begottenness of the Son does not mean, however, that the Son is a creature. Because he is the same substance (homoousios) as the Father and the Spirit, he was also uncreated.

The biblical and Christian doctrine of the Trinity is a necessary mystery to the faith so that without it, there would be no faith. It is necessary primarily because the Scriptures teach it. Because it is a biblical doctrine, the creeds teach it, and for the same reasons our theologians have taught it. Despite all the attempts by students to investigate it and despite all the attempts by critics to level it, the doctrine of the Trinity remains a glorious mystery.

Notes

  1. For example, semi-Pelagianism, whether in its Roman or Arminian form is a grave error, but it is not heresy, at least not in the same way as anti-Trinitarianism is. It is true, however, that certain modern developments in Roman dogma (e.g., the alleged assumption of the Virgin Mary) threaten seriously the catholicity of their doctrine of God.
  2. Some other well-meant but errant illustrations: the egg, forms of gold, apple, the lover, beloved and love, and the shamrock. On the dangers of such analogies, see John Calvin, Institutes, 1.13.18. Louis Berkhof gives a more favorable view of some analogies. See Louis Berkhof, Systematic Theology (Eerdmans, 1939), 90.
  3. This is true of Islam. Strictly speaking Allah is not personal. Personal speech about him is mere convention. This is true of most other forms of Unitarianism.
  4. See Peter Toon, Our Triune God: A Biblical Portrayal of the Trinity (Victor, 1996), 82–85, 90–92. See also Herman Bavinck, The Doctrine of God, trans. W. Hendriksen (Eerdmans, 1955); and Hermann Witsius, The Apostles’ Creed, trans. D. Fraser, 2 vol. (1823; [reprint: den Dulk Foundation P&R Publishing, 1993]), especially vol. 1.
  5. See Dennis E. Johnson, “Fire in God’s House: Imagery from Malachi 3 in Peter’s Theology of Suffering (1 Pet. 4:12–19),” Journal of the Evangelical Theological Society 29 (1986), 285–94. See also M. G. Kline, Images of the Spirit (Baker, 1980); Bavinck, The Doctrine of God, 255–56, 271–74.
  6. Bavinck, The Doctrine of God, 264–66.
  7. See Gerald L. Bray, “The Patristic Dogma,” in Peter Toon and James D. Spiceland, eds., One God in Trinity (Cornerstone Books), 42–61; Gerald L. Bray, “Explaining Christianity to Pagans: The Second Century Apologists,” in Kevin J. Vanhoozer, ed., The Trinity in a Pluralistic Age: Theological Essays on Culture and Religion (Eerdmans, 1997). The Chalcedonian Definition was primarily a Christological statement, but it presupposed the creedal doctrine of the Trinity.

©R. Scott Clark. All Rights Reserved.

Editor’s Note: This was originally published in a 1999 edition of Modern Reformation Magazine, and on the Heidelblog in 2012.

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  • R. Scott Clark
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    R.Scott Clark is the President of the Heidelberg Reformation Association, the author and editor of, and contributor to several books and the author of many articles. He has taught church history and historical theology since 1997 at Westminster Seminary California. He has also taught at Wheaton College, Reformed Theological Seminary, and Concordia University. He has hosted the Heidelblog since 2007.

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