It was on the Sunday after Whit Sunday (Pentecost) in the year 1162, that Thomas Becket was consecrated as perhaps the most famous Archbishop of Canterbury. It was he who subsequently decreed that the day of his consecration should be instituted as a new festival, in honour of the Holy Trinity. This feast became so important that the Anglican church has always named the long season of summer Sundays – right through until Advent, in fact – as “Sundays After Trinity”: an observance that spread from Canterbury throughout the whole of the Christian world.

Interestingly, this is the one festival in the Christian year that does not relate to particular events. Other festivals – Advent, Christmas, Epiphany, Lent, Passiontide, Easter, Ascension, Pentecost – all of these relate to specific events in Christ’s life on earth. But Trinity Sunday is different. It refers instead to the faith that we profess, of a God who is the three-in-one creator, redeemer and sustainer.

For many Christians, however, Trinity Sunday is an annual reminder of the difficulty of our faith. How can three be one? But of course, when we are dealing with faith, we are always dealing with something more than we can fully grasp or define.

The early Christian Church, however, felt that definition had to be attempted. And so evolved what has been called Christianity’s ‘new mathematics’, whereby 1 + 1 + 1 = 1: one God, ‘Father, Son, and Holy Spirit’ – which we have heard in today’s gospel reading from Matthew – the so-called ‘Great Commission’: “Go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit”.

This can be a very difficult concept to take in. And so we do one of two things: either we fall back on saying “it’s a mystery” or we attempt to define our faith in complex creeds – and whichever route we take, we are left open to criticism. It can be hard to find a way through. So as always, let’s look at what the Bible tells us. The Gospel of John is especially rich in Trinitarian language. In John 1: 29-36 we read how John the Baptist gave this testimony:

“I saw the Spirit come down from heaven as a dove and remain on him. 33 And I myself did not know him, but the one who sent me to baptise with water told me, ‘The man on whom you see the Spirit come down and remain is the one who will baptise with the Holy Spirit.’ 34 I have seen and I testify that this is the Son of God.”

In this one passage, the writer speaks of the Father (“the one who sent me”) the Spirit and the Son. Then, in John Chapter 14, Jesus tells his disciples: “the Holy Spirit, whom the Father will send in my name, will teach you everything, and remind you of all that I have said to you” (14:26). Finally, in John 16:13 we read:

13 But when he, the Spirit of truth, comes, he will guide you into all the truth.”

At Pentecost, we heard about what Jesus told his disciples: that when he was gone, the Father would send this mysterious spirit that in Greek is called Parakletos, the advocate. We have to remember that the disciples, most of whom were destined to be dragged before the courts to explain their rebellious faith, would need all the help they could get when this happened. But this is not an educated lawyer that Jesus is talking about, when he says ‘advocate’: he is talking about the Holy Spirit.

So perhaps we can begin to see how the post-Pentecostal experience of the early Church eventually led to the formal doctrine of the Trinity. At this point, I’d like to quote, as I have done before, from a sermon given by Rowan Williams on Trinity Sunday back in 2009. In it, I think, he explains very powerfully how it was that the early church came to this understanding:

“…when the disciples have stood alongside Jesus, and then failed to stand alongside him at his crucifixion, but then were recalled to stand alongside him again in his resurrection, then the risen Lord says, 'Go and do the same'. ‘Go, baptise, go and draw people into the mystery of the threefold love. Go and draw people to stand in my place and pray with my prayer and breathe with my spirit.’ And they do.

And out of that, comes the teaching. Out of that experience … comes the doctrine. Because if you try long enough to stand in that place where Jesus is … sooner or later you'll begin to search for the words that might begin, just a little, to do justice to this mystery – and you will understand that you stand with the Son, crying out to the Father, borne up by the Holy Spirit. And bit by bit, the Church of God learns that language and begins to teach that doctrine.”

I think that Rowan Williams helps us here to understand how it was that the Church came to the conclusion that there is an inseparable link between God the Father, the creator-judge; Christ the redeemer; and the Holy Spirit, who gave the first Christians the power at Pentecost to take their faith out into the world.

This Holy Spirit is described by Paul (in Galatians Chapter 5) not in terms of fire and wind and speaking in tongues, but in terms of the “Fruit of the Spirit”: “Love, joy, peace, kindness, generosity, faithfulness, gentleness and self-control”. Whenever we seek meaning in our lives, a search for sense and grace, these are the qualities – the gifts of the Spirit – that help us to become more fully human. And when we fall short of our human potential, as we surely will - but still receive forgiveness and a renewed determination to live a more purposeful life; it is then we have an experience of salvation.

Creation, revelation, salvation: a powerful example of the Trinity made real.

So on this Trinity Sunday, let us pray:

Lord, we pray that day by day we might, little by little, become more Christ-like people:

People who praise God the Father, the creator, who gave us bodies to live in this created world;

People who praise God the Son, who through his incarnation, his life, teaching and suffering, brought us salvation;

People who praise God the Spirit, who leads us beyond this world – and into eternal life.