The doctrine of the Trinity, simply stated: There is One God and this One God is three "persons," Father, Son and Holy Spirit. The three persons of the Trinity are equally God, "co-equal and co-eternal," we say. One is not more divine than another. One is not subordinated to any other.
But God is not simply a category with three members. Father, Son and Holy Spirit are single substance. They have a single will, a single energy. There are not three Gods, but only one God.
The question for us today is: Do we still need the Trinity? This peculiar doctrine manages to combine two thing many of us like to avoid -- technical jargon and mathematics. The technical terms are not hard to say, but they have very specialized philosophical meanings: Substance, Person, Co-eternal. As for trinitarian mathematics, the good news is that the numbers don't get very big. You never go over the number three. The bad news is that this is mathematics like we've never seen. Like something out of Alice in Wonderland, it doesn't follow any of the rules. Three equals one and one equals three.
More disturbingly, the doctrine of the Trinity seems to attempt to describe the inner life of God -- the relation of the three Persons, in themselves, one to another -- and this is something we mortals really don't know anything about and, even if we could know about it, we don't see how it could affect us. So, the questions remains: Do we still need the Trinity?
Before we dispense with the doctrine altogether, we really ought to look at the Bible. Naturally, the passages of Scripture which best relate to the doctrine of the Holy Trinity are those appointed for this feast of Trinity Sunday. For instance, we just heard St. Paul assure the Romans that when they cry out to God "Abba, Father!" it is the Holy Spirit bearing witness that we are children of God, and joint heirs with the Son of God, the Christ. The Spirit bears witness to our kinship with the Father and our fraternity with the Son.
Similarly, our reading from St. John's Gospel combines the Spirit, who births us into the kingdom of God, with the Son of Man who descended from heaven, with the God who loved the world so much that he gave his only Son.
Granted, the connections between Father, Son and Spirit are not very clear or very close in the passages. In fact, all three persons never even manage to fit into the same sentence. The lessons appointed for other years in our lectionary are much tidier in this respect. For example, the Epistle for year A closes with the splendid conclusion of Second Corinthians: "The grace of the Lord Jesus Christ, the love of God, and the communion of the Holy Spirit be with all of you." Here we have Jesus Christ, God and Holy Spirit all together in one breath. The Gospel for year A is the Great Commission from St. Matthew and this reading is as "trinitarian" as the Bible ever gets. The Risen Christ directs the Eleven to "go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit."
However, the theologians would say that even this last passage is not trinitarian but merely "triadic." In other words, the three names -- Father, Son and Holy Spirit -- are mentioned, but nothing is said about their relationship. Nothing about three in one or one in three. Nothing about God in three persons. The word "Trinity," of course, never appears in the Bible. All of that language came a couple of centuries later.
Nevertheless, I think that the doctrine of the Trinity is going to stay with us because it has a mystery of great importance to reveal to us, something more than just the inner workings of the divinity. First of all, the doctrine states that we believe in a personal God. You won't find "personal God" in the Bible either, but that concept has emerged from the experience of believers over centuries. Yes, we do believe in a personal God, for we believe in God in three persons. The word is carefully chosen. It means, above all, that God is cognizant of us and loves us. And it means that we are able to love God, intensely and wholeheartedly.
Second, the doctrine of the Trinity affirms that God does not exist in isolation. God is a social God. Even prior to the creation, God existed in relationship, the relationship, the relationship of the Father, Son and Holy Spirit one to another. Since we are created in God's image, the means that we are created for relationship as well. We become whole persons only in relationship to one another and to God.
Finally, we need to observe the traditional language about the Trinity (and this is from the Athanasian Creed): The three persons are Co-equal and Co-eternal. They exist in communion, in a mutual sharing of life. The persons of the Trinity do not allow for inequality, or subordination, or domination, or hierarchy. Our Baptism into the Church in the name of the Trinity means that all of us, though irreducibly unique, exist together as equal partners in Christ in a relationship of mutual love.
Perhaps that is why Paul's prayer that "the grace of the Lord Jesus Christ, the love of God and the communion of the Holy Spirit be with you all" flows out of Paul's appeal to the Corinthians to live in peace and to greet one another with a holy kiss. The loving mutuality of the Church has its source in the loving mutuality of the eternal Trinity.
So, do we still need the Trinity? We might just as well ask: Do we still need mutuality? Do we still need to be in relationship? Do we still need a personal God? Do we still need love? AMEN