The Trinity is not a secondary way of talking about the Christian God within the framework of monotheism, but is in fact the very identity of the Christian God. Robert Jenson even argues “that the phrase ‘Father, Son, and Holy Spirit’ is a proper name for the God whom Christians know in and through Jesus Christ,” and I think that is right.
So in my view monotheism is not a very good starting point to think about the Christian God, although it has often been done. The Western theological tradition has often fallen into a residual Monarchianism, “a tendency to resolve a doctrine of the Trinity in the implicitly unitarian direction of a single and inscrutable divine sovereignty.” (The quote is from John E. Colwell’s Promise and Presence referring to his teacher Colin Gunton’s book The One, The Three, and The Many. And Gunton was a student of Jensen, so there is an intellectual lineage at work here).
The Trinity, in my view, is an inference from the Trinitarian shape of the Gospel narratives, and therefore (although never named as such in scripture) the most biblical of doctrines, even if it took centuries to develop. My friend Willis Elliot, in an e-mail to me about the development of the doctrine of the Trinity, affirms that even the process itself is Spirit-guided:
“From first-stage subordinationism to final stage trinitarianism is a long stretch, too long for Arius and most Christians until after Nicea AD325CE, the council at which Athanasius’ Greek-language Bridge to the Trinity won the day and persuaded Constantine to decide against Arius. It would have been a bridge too far for Augustine’s Latin unaided by the Latinization of Athanasian metaphysics: like Hebrew and Aramaic, Latin did not have the capacity to receive and convey the orthodox Christian doctrine of God. God’s choice of Greek as the founding vehicle of the Christian mind was itself revelational.”
But why a Trinity? Well, if God is God then obviously every form of dualism must be rejected. But God is also love, and love requires some manner of plurality within the divine unity. The Gospel story is a love story among the persons, a love spilling out beyond itself for us. Perhaps this is best apprehended in liturgy, where we pray “to the Father, through the Son, in the Spirit.”
“We pray our prayers to the Father ‘through Jesus Christ our Lord,’ because it is through his Son made man as Jesus of Nazareth that God has shown himself to us. In the words and deeds, in the life, death and resurrection of Jesus we know what God’s attitude towards us is and that he is prepared to reclaim and remake us for himself. That is why Christians worship God not as a remote and distant mystery shrouded in the glory of his deity, but as the one who in his love has come to us, lived among us, died for us and triumphed over our enemies.”(The Forgotten Trinity, p. 5-6)
So the Gospel story is not merely the story of Jesus, but rather the story of Jesus’ relatedness to the Father through the Spirit, and the Father’s relatedness to the Son through the same Spirit. As Colwell puts it:
“The words and actions of the Son are the words and actions of the Father mediated by the Spirit. There is no action within the narrative that is not an action of the undivided Trinity. There is no action within the narrative that is not an action mediated by the Spirit. The Father’s love and calling to the Son is mediated by the Spirit at Jesus’ baptism. The ministry of Jesus is a demonstration of the Father’s kingdom in the power of the Spirit. The sacrifice of the Son is mediated to the Father by the Spirit. The Father’s raising of the son from the dead is mediated by the Spirit. At every point the Spirit is the agent of mediation between Father and Son.” (Colwell, p. 37)
This peculiar way we Christian’s have of thinking about and speaking about God is yet another “scandal of particularity.” Which is why interfaith dialogue (which I’m all for) that uses monotheistic commonalities as the starting point typically sells out Christianity’s particular understanding, and settles for a kind of a “theism plus Jesus.” But that view pervades our churches, too, so its not just outsiders who have trouble with the Trinity.
We teachers in the church share some blame for that. Nevertheless, the one God’s Triune self-relatedness is the true grammar of a Christian theology that would do justice to the Gospel narrative and give true definition to the language of grace. The Christian God really doesn’t make much sense without it.