For our Jewish and Muslim cousins, to-day offers proof positive that we Christians are either confused or deluded. We say we join with them in worshipping the one, true God whom they call El Adonai or Allah, and then we tell them there is God the Father, and God the Son and God the Holy Spirit. There you are, they say: you have three gods, not one. And it does seem a bit odd to have a special feast day each year for a doctrine rather than a saint, or Jesus.
In the first few centuries of Church history, Christians argued and fought over this very point. They had all kinds of ideas. Perhaps the Son was a man adopted by God and not God himself. Perhaps Jesus was some kind of avatar or illusion, like a mirage portraying God, but not actually being God. Perhaps the Holy Spirit is not actually God, but Jesus in resurrected form.
These arguments and dissensions have not really stopped: they were certainly at work in this country in the 16th, 17th and 18th centuries, and the arguments continue to this day. It would take a better preacher than I to explain in short compass how we might resolve this conundrum. I venture to say that it cannot be resolved because if we could resolve it, we would have defined God. And any God we can define is not a God worthy of worship.
In short, the Christian doctrine of the Trinity is the best attempt we can make to put into words an irreducible mystery, something that will always be hidden until such time as we behold God face to face – at which point we shall not care about doctrine, because we shall be lost in wonder, love and praise.
In the meantime, we continue to worship God the Source of all being; God the eternal Word from before the Big Bang; and God the Spirit whose inspiration fills every part of the cosmos, giving life and bringing all into the loving purpose of God. In the words of that lovely Celtic hymn, “I bind unto myself this day the strong name of the Trinity”. I believe in one God.