A few weeks back I started what I hope will be a short series on the Trinity. In writing, there is no shortage of material regarding God as Trinity. But in the local church, at least from my own experience, teaching on what is most fundamental to God’s nature is scant. Furthermore, when we do teach or preach on the Trinity, it typically remains abstract, giving the impression that God’s Triune essence is unimportant or impractical—or both. So one of the aims for my short series is to demonstrate that the doctrine of the Trinity is a life-giving and faith-building aspect of what we believe, in addition to taking us deeper into the God we profess to know.

Q5 of the Westminster Shorter Catechism (WSC) asks: “Are there more Gods than one?” The answer goes: “There is but one only, the living and true God.” But the answer to Q6 reads: “There are three persons in the Godhead: the Father, the Son, and the Holy Spirit; and these three are one God, the same in substance, equal in power and glory.” My purpose for this post is to consider what it might mean that God is both one and three. We will consider those respectively, under the following two headings.

“There is but One Only”

Off the bat, there are countless places throughout the Bible that emphasise God’s oneness, singularity, and exclusive divinity; that there is only one God. For example, consider the Jewish Shema, “Hear, O Israel: The Lord our God, the Lord is one” (Deuteronomy 6:4; also 4:35). This is echoed in Solomon’s dedication of the temple (1 Kings 8:59-60). The prophet Isaiah also defaults to this language: “Thus says the Lord, the King of Israel and his Redeemer, the Lord of hosts: ‘I am the first and I am the last; besides me there is no god. Who is like me?’” (Isaiah 44:6-7; 45:5-6). Centuries later, Jesus would say: “I and the Father are one” (John 10:30).

The implications of this teaching are simultaneously straightforward and unsettling. They are summarised well in the first and second commandments (Exodus 20:3-6), which the New City Catechism succinctly unpacks in Q9: “First, that we know and trust God as the only true and living God. Second, that we avoid all idolatry.” Taken together, God’s oneness is a corrective both to what we worship and where we locate our confidence. Our lives are crowded out, with so many things competing for our affections and inviting us to believe in them. Our world is full of good things, which cannot fulfil their promises to satisfy our hearts and provide true security. But the “one…living and true God” can, if we will delight and sink our faith deeper into him.

“There are Three Persons”

Though the answer to WSC Q5 is emphatic that there is only one God, Q6 says: “There are three persons in the Godhead: the Father, the Son, and the Holy Spirit; and these three are one God, the same in substance, equal in power and glory.” In the next post I will explore the language of “substance,” but for now I want to focus on the significance that God exists eternally as “one God” and “three persons.” Theologians far cleverer than myself have answered the charge that such claims are illogical or self-contradicting. So I’m content to sidestep it for the time being to consider the implications of knowing God as “divine community,” and the significance of that for understanding ourselves.

Firstly, God doesn’t create from a place of need. It was not the lack of, nor a longing for, community that moves God to make other beings. Though he does invite his creatures—that’s you and me—into fellowship with him, this invitation comes from a God who is relationally full, even overflowing. As John Webster writes, “It is Father, Son, and Spirit that God is of himself, utterly free and full, in the self-originate and perfect movement of his life; grounded in himself.” Thus, later in the same essay, Webster can say, “What God is and has of himself is life and this life includes a self-willed movement of love.” This “movement of love” is first and fully experienced within the Godhead, between Father, Son, and Spirit. Thus when it is extended to what God has made it is an overflow of that same love.

Secondly, sticking with the theme of love, in his Reason for God, Keller argues that if God is “unipersonal” then love couldn’t have existed until the moment of creation, which provided an object for God’s love. Love is something only truly shared or expressed between persons, from one to another. A singular and therefore isolated deity cannot appropriately be love. Because loving relationships within the Godhead are the source and centre of creation, Keller continues: “Love is the purpose of God because he is essentially, eternally, interpersonal love.” God has woven love into the fabric of reality, because “God is love” (1 John 4:16). When we live with ourselves at the centre, prioritising self-love or making our own love conditional, we work against God’s purposes.

Finally, unpacking the previous point, that God is love and we are made in his image, has profound implications for understanding of human flourishing. In Introducing Covenant Theology, Michael Horton writes: “God’s very existence is covenantal: Father, Son, and Holy Spirit live in unceasing devotion to each other…Created in the image of the Triune God, we are by nature outgoing, interdependent, relationship establishers, finding ourselves in the other and not just in ourselves.” Reread Horton’s last sentence: we find ourselves in the other rather than ourselves. Furthermore, that “other” is plural, referring to community. Created in God’s image means that we only properly discover and express ourselves when we give ourselves to others.

“Know Thyself”

As I said in my introduction, teaching or preaching on the Trinity is typically abstract and impractical. I hope that I’ve gone some way in correcting that trend above. Firstly, considering God’s oneness we learnt not only why idolatry is wrong but also why it is so destructive to personal faith. Secondly, encountering God as three—or as a divine community of persons—we were better equipped for thinking about human purpose and flourishing, since we’re made in the image of God. I shall give Calvin the final word: “It is certain that man never achieves a clear knowledge of himself unless he has first looked upon God’s face, and then descends from contemplating him to scrutinise himself” (Institutes 1.1.2).