When the fullness of God’s self-revelation in Scripture is not taken into account, heresy is the result. Those who emphasize the oneness of God to the neglect of what Scripture teaches regarding the deity of the three persons fall into errors such as Adoptionism, Modalism, and Arianism. Those who fail to grasp what it means to say that the Father is God, the Son is God, and the Holy Spirit is God, fall into various forms of subordinationism. Those who emphasize the three to the neglect of what Scripture teaches about the oneness of God fall into forms of tritheism.

This I commit unto you to-day; with this I will baptize you and make you grow. This I give you to share, and to defend all your life, the One Godhead and Power, found in the Three in Unity, and comprising the Three separately, not unequal, in substances or natures, neither increased nor diminished by superiorities or inferiorities; in every respect equal, in every respect the same; just as the beauty and the greatness of the heavens is one; the infinite conjunction of Three Infinite Ones, Each God when considered in Himself; as the Father so the Son, as the Son so the Holy Ghost; the Three One God when contemplated together; Each God because Consubstantial; One God because of the Monarchia. No sooner do I conceive of the One than I am illumined by the Splendor of the Three; no sooner do I distinguish them than I am carried back to the One. When I think of any One of the Three I think of Him as the Whole, and my eyes are filled, and the greater part of what I am thinking of escapes me. I cannot grasp the greatness of that One so as to attribute a greater greatness to the Rest. When I contemplate the Three together, I see but one torch, and cannot divide or measure out the Undivided Light.

In chapter 17 of the first book of his Institutes of the Christian Religion, John Calvin expresses his delight in this passage written by the fourth-century Cappadocian church father Gregory of Nazianzus. Specifically, Calvin points to the following sentence: “No sooner do I conceive of the One than I am illumined by the Splendor of the Three; no sooner do I distinguish them than I am carried back to the One.” Why the delight in these words? Because Calvin recognizes that when we think about our triune God, we are thinking about a truth that is ultimately beyond our complete grasp. He understood that if we are to avoid error in our thinking and speaking about God, we have to be very careful and thoughtful.

Gregory of Nazianzus (AD 329–390) was one of the greatest theologians of the early church. He was instrumental in the resolution of the fourth-century Trinitarian crisis that engulfed the church. Certain of his writings, particularly Orations 20, 23, 25 and the five theological orations (27–31), are foundational works in the history of Trinitarian theology. Gregory understood that Trinitarian heresies were the result of a failure to take into account the fullness of God’s self-revelation in Scripture.

When we turn to Scripture, we find several truths about God revealed. All of them must be taken into account if we are to speak truthfully. First, there is only one God. “To you it was shown, that you might know that the Lord is God; there is no other besides him” (Deut. 4:35). This fundamental truth is revealed multiple times in both the Old and New Testaments. It stands in direct contrast to the polytheism that was rampant in the ancient world. “Hear, O Israel: The Lord our God, the Lord is one” (Deut. 6:4). There is only one true God.

Second, this God is the Father of the Lord Jesus Christ. “Blessed be the God and Father of our Lord Jesus Christ, the Father of mercies and God of all comfort” (2 Cor. 1:3). In other words, when Jesus speaks of His Father, He is speaking of the one God. “This was why the Jews were seeking all the more to kill him, because not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God” (John 5:18; see 17:1–5). In short, according to Scripture, the Father is God.

Third, in numerous ways, Scripture reveals that Jesus Christ is God. “In the beginning was the Word, and the Word was with God, and the Word was God. . . . And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth” (John 1:1, 14). Both Paul and Peter speak of our “God and Savior Jesus Christ” (Titus 2:13; 2 Peter 1:1). To Him are given titles that belong only to God (for example, Isa. 44:6; 48:12; see Rev. 1:8; 22:12–13). He does works that only God can do (for example, Matt. 9:1–8). According to Scripture, the Son is God.

Fourth, Scripture reveals that the Holy Spirit is God. There is no one and nothing other than God who is eternal, yet the Holy Spirit is revealed to be the “eternal Spirit” through whom Christ offered Himself to God the Father (Heb. 9:14). Peter indicates that to lie to the Holy Spirit is to lie to God (Acts 5:3–4). There is one God. The Father is God. The Son is God. And the Holy Spirit is God.

Fifth, Holy Scripture reveals that the Father, Son, and Holy Spirit are distinct. The Father is not the Son. “All things have been handed over to me by my Father, and no one knows the Son except the Father, and no one knows the Father except the Son and anyone to whom the Son chooses to reveal him” (Matt. 11:27). Jesus prays to the Father (for example, John 11:41–42), an action that would be a farce were the Father and Son merely two modes of the one God. He is our advocate with the Father (1 John 2:1). The Father is not the Son, and the Son is not the Father. The Son is also not the Holy Spirit. The Holy Spirit descends upon the Son (Luke 3:22). Jesus sent the Holy Spirit (John 15:26; 16:7), who is another Comforter (John 14:16 KJV). The Son and Holy Spirit (and the Father) are distinguished in the Great Commission (Matt. 28:19). The Father is not the Holy Spirit. The Father sends the Spirit (John 14:16; 15:26). The Spirit intercedes for us (Rom. 8:26–27).

When the fullness of God’s self-revelation in Scripture is not taken into account, heresy is the result. Those who emphasize the oneness of God to the neglect of what Scripture teaches regarding the deity of the three persons fall into errors such as Adoptionism, Modalism, and Arianism. Those who fail to grasp what it means to say that the Father is God, the Son is God, and the Holy Spirit is God, fall into various forms of subordinationism. Those who emphasize the three to the neglect of what Scripture teaches about the oneness of God fall into forms of tritheism.

Gregory’s quote reveals how carefully we have to think about our triune God. He describes a kind of perpetual conscious oscillation between thinking of God as one and thinking of God as three. He deems this necessary because our minds cannot fully grasp both truths simultaneously and we have a tendency to stop at one or the other, thus becoming either practical Unitarians or practical tritheists. John Calvin delighted in this quote because, like Gregory, he understood that there is an element of mystery involved in the doctrine of the Trinity. He also understood that this mystery should not elicit a feeling of skepticism about what God has revealed. Instead, it should elicit wonder and worship. Gregory’s words beautifully express this sense of awe and adoration. With Calvin, we too can learn from and delight in them.

Dr. Keith A. Mathison is professor of systematic theology at Reformation Bible College in Sanford, Fla. He is author of several books, including From Age to Age. This article is used with permission.