In the name of the Father and of the Son and of the Holy Spirit. Amen.

The disciples gather on the mountain in Galilee, and there the risen Jesus gives what we know as the Great Commission:
“Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.”
Not names — plural — but name, singular. One God: Father, Son and Holy Spirit.

And there, at the end of Matthew’s Gospel, we are brought into the very heart of the mystery we celebrate today: the mystery of the Holy Trinity.

Now if we are honest, Trinity Sunday can sometimes feel intimidating. People speak about it as though it were a mathematical puzzle to solve or a theological examination to pass. Three in one and one in three. Not three gods, but one God. Distinct persons, yet one being. And before long our heads begin to ache.

But the doctrine of the Trinity is not meant to confuse us. It is meant to draw us into wonder. It tells us something profoundly important about who God is.

God is not solitary.
God is love.

Before ever the world existed, there was relationship: the Father loving the Son, the Son delighting in the Father, the Spirit binding them together in eternal communion and joy. Creation itself flows out of that love.

That is why Isaiah can speak with such awe of God’s greatness:

“Who has measured the waters in the hollow of his hand?”
“Who has directed the Spirit of the Lord?”

The prophet stands amazed before the majesty of God. Nations are like a drop in the bucket before him. The islands weigh no more than fine dust. God is beyond our measuring, beyond our controlling, beyond our comprehension.

And yet this same God knows his people personally.
This same God “gives power to the faint.”
This same God renews the strength of those who wait upon him.

The God who holds the oceans in his hand also holds us in his love.

And perhaps that is the key to Trinity Sunday. The Trinity is not an abstract theory about God. It is the living truth that the God who made us, redeemed us and sustains us is eternally loving relationship.

Which means that relationship lies at the very centre of what it means to be human too.

In a passing but striking phrase in his recent encyclical Magnifica humanitas, Pope Leo XIV reflects on the dignity of humanity as bearing the image of God — not merely as isolated individuals, but as persons created for communion, fellowship and self-giving love. That insight resonates deeply with Trinity Sunday. If we are made in the image of the Triune God, then we are made not for selfishness or isolation, but for relationship: with God and with one another.

That matters enormously in our fragmented world.
We live in an age where people are increasingly lonely, increasingly divided, increasingly suspicious of one another. Community becomes fragile. Families strain. Nations polarise. Even the Church can struggle to live together in charity.

And so St Paul’s words to the Corinthians become especially powerful:
“Put things in order, listen to my appeal, agree with one another, live in peace; and the God of love and peace will be with you.”

Notice that phrase carefully: “the God of love and peace.”
Paul is not simply giving moral advice. He is saying that Christian unity reflects the very life of God himself.

Every act of forgiveness, every kindness, every reconciliation, every moment of patience or compassion becomes a small reflection of the Trinity.

That also shapes how we understand the Church’s mission. Jesus does not simply send the disciples out with instructions. He sends them out in the life of the Trinity:
“Baptizing them in the name of the Father and of the Son and of the Holy Spirit.”

The Church exists to draw people into the very life of God.

Not simply into religion.
Not simply into morality.
But into communion with the living God.

And that mission begins with worship. Every time we come together we hear the words “In the name of the Father and of the Son and of the Holy Spirit”, every time we baptise, every time the priest pronounces the blessing every time we say the words “The grace of the Lord Jesus Christ, the love of God, and the fellowship of the Holy Spirit be with you all” — we are being reminded who God is and who we are called to become.

People shaped by grace.
People shaped by love.
People shaped by fellowship.

Of course, we shall never fully understand the Trinity this side of heaven. St Augustine once said that if you think you have completely understood God, what you have understood is not God.

And yet we do not need to solve the mystery in order to live within it.

A child may not understand how sunlight works, yet still stand in its warmth.

So too with the Trinity. We may never fully explain God, but we can live in his love. We can worship in wonder. We can trust the Father who created us, the Son who redeemed us, and the Spirit who sustains us.

And perhaps that is enough for Trinity Sunday:
not that we finally explain God,
but that we fall down before him in awe,
and hear again the promise of Christ:

“Remember, I am with you always, to the end of the age.”