Last week, a student asked me about a challenge she received from a Muslim: Why does it matter if God is a Trinity? I’ve written before about how God’s Trinitarian nature affects prayer (I highly recommend the book quoted in that post, Delighting in the Trinity ), and here’s more from Justin Dillehay on “Two Reasons the Trinity Matters”:
[T]he kind of God we have determines the kind of relationship we will have with him.
For example: Is your God an all-sufficient fountain of joy and love with an inexhaustible supply available for you anytime? Or did your God create you and save you because he was lonely and needed you? It depends. Is your God the unitarian God of Arianism (think Mormons and Jehovah’s Witnesses), modalism, or Islam? Or is he the biblical three-in-one? The God of John’s Gospel was never lonely, because even in the beginning, before anything made was made, he already had someone with him. “The Word was with God” (John 1:1).
This is good news, because it tells us God didn’t create us because he needed somebody to love. He wasn’t without family. He was already a Father. And he already had an eternally begotten Son, the radiance of his glory and the exact imprint of his nature (Heb. 1:3), lying in his bosom (John 1:18) and basking in his love (John 17:24). You and I aren’t the result of some man-shaped hole in the Father’s heart; rather, you and I represent the overflow of the Father’s eternal love for his Son - as though the Father had said, “Son, this love of ours is just too good to keep to ourselves. So together with our eternal Spirit, let us make man in our own image, so that others might see and experience our love, and so that you might be the firstborn among many brothers” (cf. Gen. 1:26; Rom. 8:29).
Is the Trinity practical? Let me ask you - what kind of salvation does your gospel give you? A judge who forgives your sins? Not bad. But not good enough. The triune gospel is better by far. It’s God giving himself to you in creation and redemption. The same Son who was begotten by the Father before all worlds was sent by the Father into this world, to live and die for us and our salvation. And the same Spirit who proceeded from the Father and the Son from all eternity was sent by the Father and the Son into this world, to live inside us and bring us to Christ - and through Christ to the Father - so that we might be taken into his family, surrounded by his life and love, to glorify and enjoy him forever.
It’s more than forgiveness. It’s joining an eternal family. It’s being conformed to the image of the Son by the Spirit (Rom. 8:29) and becoming a partaker of the divine nature (2 Pet. 1:4). In short, it’s the kind of salvation that only the trinitarian God can offer.
Read the rest of what he has to say here, and see, also, “Our Existence as Relational Beings Points to the Trinity.”