Christian praise of the Trinity is praise of the one God. The oneness of God is intrinsic to the first and greatest commandment of the Old and New Testaments. Moses proclaims God’s oneness and calls Israel to acknowledge God’s singular worth by loving him with all their heart, soul, and might (Deut. 6:4–5). Jesus affirms God’s oneness as “the most important” commandment of all (Mark 12:28–29) and says that a scribe’s profession of God’s oneness evidences his proximity to God’s kingdom (Mark 12:34). Christians are baptized into “the name” of the one God (Matt. 28:19), and Christians confess the name of the one God (1 Cor. 8:6). “The Lord is one” (Deut. 6:4).
The Christian doctrine of the Trinity is teaching about the one God, the author and end of all things; about the relations between the Father, the Son, and the Holy Spirit that constitute the one God’s inner life; and about the manner in which the one God extends those relations to his people through his works of creation, redemption, and consummation, to the praise of his glory. Christian teaching about the one God includes teaching about his “unity of singularity” and teaching about his “unity of simplicity.”1 God’s unity of singularity means that God alone is God and there are no other gods but God. God’s unity of simplicity means that God is one with himself, self-same and indivisible in his being and operations, and God is not composed of parts. God is pure God, and nothing but God is God.2
It is tempting to think that the doctrine of the Trinity is concerned only with God’s “threeness” and not with God’s oneness. But to succumb to this temptation would be a terrible mistake. The doctrine of divine unity in general and the doctrine of divine simplicity in particular are central to an orthodox Christian confession of the Trinity. The doctrine of divine simplicity further elucidates the basic grammar of the Bible’s Trinitarian discourse by helping us better appreciate the kind of oneness that characterizes God’s triune life, by helping us more deeply affirm the full divinity of the persons of the Trinity, and by helping us better grasp what distinguishes the persons of the Trinity from each other.
“This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all” (1 John 1:5). This truth, taught by Jesus, heard by John, and proclaimed to us in apostolic writing, summarizes basic Christian teaching about divine simplicity. God is identical with light, and God is nothing but light. The truth taught in this verse also exhibits the basic grammar of divine simplicity, providing us with a “standard” (Rom. 6:17) or “pattern” (2 Tim. 1:13) to guide our thinking and speaking about the simple God. God is identical with his perfection, and he is wholly perfection, without any mixture of imperfection. He is wisdom, and in him is no folly at all. He is goodness, and in him is no evil at all. He is power, and in him is no weakness at all. He is being, and in him is no nonbeing, no unfulfilled being at all.
The identity of God with God, and the lack of all composition in God, is what Christians affirm when they confess the doctrine of divine simplicity. Johannes Wollebius (1589–1629) offers a representative summary of Christian teaching on divine simplicity that can help us further appreciate the meaning of the doctrine. According to Wollebius, to confess a simple, noncomposite God is to say, “He is not compounded of parts, or of genus and species [differentia], or of substance and accidents, or of potentiality and act, or of being and essence.”3
1. God is not composed of parts.
Unlike human beings, God is not a composite of body and soul. God is spirit, not flesh (Isa. 31:3). Nor is God composed of metaphysical parts. God is not part light and part darkness, part this and part that. God is pure and unmixed light (1 John 1:5), pure and unmixed being, pure and unmixed wisdom, pure and unmixed goodness, pure and unmixed power. Divine simplicity, thus understood, follows from divine spirituality—“God is spirit” (John 4:24).
2. God is not composed of genus and species.
As we saw in an earlier chapter, there is no larger category of gods of which the Lord is a member. “YHWH is the God” (Deut. 4:35, my trans.). Nor do God and creatures together compose a larger category of things (beings, persons, etc.) of which God is a greater version and creatures are lesser versions. God is not just a greater version of this or that kind of thing. The God who created all things transcends the categories of all created things. Indeed, he transcends categorization altogether. Divine simplicity, thus understood, follows from God’s transcendent, categorical uniqueness (Ps. 135:5; Isa. 40:18). God is the incomparable one.
3. God is not composed of substance and accidents.
God does not have attributes in the way we have attributes. We possess specific attributes or qualities, such as wisdom or brown hair, that are metaphysically distinct from ourselves. We can grow or decrease in wisdom or lack wisdom altogether. Yet we still remain who we are as wiser, less wise, or unwise versions of ourselves. The color of our hair can change, or our hair can fall out altogether. Yet we still remain who we are. Many of our qualities and attributes do not inhere in us essentially. To be Scott is not essentially to be right-handed. To be Scott is not essentially to have brown hair, or even to have hair at all. Not so with God. God is identical with the perfections we attribute to him. God is light (1 John 1:5). God is love (1 John 4:8). God is the truth. God is the life (John 14:6). Who God is and what God is are identical. He is who he is (Ex. 3:14). This is divine simplicity in the strict and proper sense. God is the great “I am.”
4. God is not composed of potentiality and act.
Unlike creatures, in God there is no potential for growth, diminishment, or change (Ps. 102:25–27). God does not gain or lose perfection (Job 22:2–3; 35:6–7; 41:11; Rom. 11:33, 35). God is not metaphysically divisible from what he once was or what he one day will become. He is “the same” yesterday, today, and forever (Heb. 13:8), the one “who was and is and is to come” (Rev. 4:8). With him “there is no variation or shadow due to change” (James 1:17). Divine simplicity, thus understood, follows from divine immutability. God is the selfsame one.
5. God is not composed of being and essence.
What a creature is (e.g., a dog, a cat, a snake) and that a creature is are metaphysically distinct. What a creature is does not entail its existence. In fact, we can imagine many kinds of creatures (e.g., unicorns, leprechauns) that do not in fact exist. Not so with God. What God is and that God is are identical. He is “the one who is” (see Ex. 3:14 LXX; Rev. 4:8), the consuming fire who does not rely on any fuel outside himself in order to burn (Ex. 3:2–3). God has “life in himself” (John 5:26). Divine simplicity, thus understood, follows from divine self-existence. God is the self-existent one.
- Herman Bavinck, Reformed Dogmatics, ed. John Bolt, trans. John Vriend, vol. 2, God and Creation (Grand Rapids, MI: Baker Academic, 2004), 170.
- Paraphrasing William Desmond: “God is God and nothing but God is God” (Desmond, God and the Between [Oxford, Blackwell, 2008], 50).
- Johannes Wollebius, Compendium Theologiae Christianae, in Reformed Dogmatics: J. Wollebius, G. Voetius, F. Turretin, ed. John W. Beardslee (Eugene, OR: Wipf & Stock, 2009), 39