Trinity Sunday, Year C (2025) - Fr Matthew Boland, OP

Today we celebrate the greatest mystery of our Faith, the mystery of the Most Holy Trinity, the mystery of God’s inner life. In one way, this mystery is very familiar to us. It permeates every aspect of our Faith—we invoke the Trinity every time we make the Sign of the Cross; we baptise in “the name of the Father, and of the Son, and of the Holy Spirit;” and we finish every decade of the Rosary with “Glory be to the Father, and to the Son, and to the Holy Spirit …”

And yet, this mystery is ineffable. It was hidden from mankind until the coming of our Lord and Saviour, Jesus Christ. Only he has revealed to us the mystery of God’s own nature. St John tells us at the beginning of his Gospel: “No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known.” This mystery which is revealed to us is that God, while being perfectly one, is also three: Father, Son, and Holy Spirit, three in one, perfect union in perfect communion. Even now, we do not grasp it directly; that will not take place until we behold God in the beatific vision, that is, in heaven. As St Paul tells us, “now we see through a glass, darkly; but then face to face.”

We should differentiate between a riddle and a mystery. A riddle is something we “work out,” something we come to the end of. A mystery is something we dwell on—a truth which grows ever deeper. While we cannot grasp this mystery directly in this life, we can meditate on it. Relying on the great theological tradition of the Church, there are a few things we can say to deepen our understanding this greatest of mysteries, through a sort of reflection, “through a glass, darkly.”

How can God be one and three? How can anything be one and many? We already have some idea of how this takes place in our world. Many philosophers have reflected on this throughout history. For example, we wouldn’t be able to say “all human beings,” unless there were something common to us all, something which makes us one, one human race, something we all share. We might call this “human nature.”

But if human nature is what makes us one, there must also be a principle of difference between us. In our case, what makes us different is our matter, our bodies. Each one of us is an instance of humanity in an individual body.

Now, God’s nature, like humanity, is one; but he can’t be individuated by matter because he is, of course, immaterial. Remember what Jesus said to the woman at the well, “God is Spirit, and those who worship him must worship in spirit and in truth.” We know that he is one—one divine nature; but there’s no matter in God. No physical material. So, what individuates the Persons of God?

St Thomas tells us that what individuates the Persons of the Trinity, what makes one Person different from the other Persons, is pure relation. This is why God names himself “Father” and “Son.” If we reflect on it, we see that these are relative terms. The word “father” only makes sense if he is the “father-of” someone; it includes in its meaning a reference to the son. It is the same for “son.” Every son is a “son-of.” The Father and the Son are pure “being towards” one another—pure relation. Now, where there are two Persons, perfectly united in the divine nature, they love one another, that is, they breathe forth Love, which is the procession of the Holy Spirit; he is the bond of love uniting Father and Son. These three, co-eternal, co-equal in power, perfectly one, perfectly three, are the Most Holy Trinity, Father, Son, and Holy Spirit. Somehow, this truth is at the heart of all truths, natural and supernatural.

What does this mean for us? We received this Spirit at Baptism, the Spirit of the only-begotten Son, the Love of God. This is why St Paul can say to the Romans, speaking of their Baptism, “the love of God has been poured into our hearts through the Holy Spirit who has been given to us.” By this Spirit we share in Christ’s son-ship, because the Holy Spirit is the Spirit of the Son, and everyone who has this Spirit is a son or daughter of God; Jesus is Son by nature, we by adoption, by sharing in his Spirit.

Now that we share in Jesus’s sonship and are sons and daughters of God our Father, we can love by the Spirit of God, the Holy Spirit. First of all, we can love God with a divine love, as his children. But God loves not only himself, but his creation. And so, we are called to love his creation with a divine love, especially other human beings, as our Lord taught us. In fact, this is simply the commandment he gave us at the Last Supper when he said to the disciples, “As the Father has loved me, so have I loved you; abide in my love. … This is my commandment: love one another as I have loved you.” That is, love one another with the love of God, which is the Holy Spirit.

To close this reflection, let us listen to the words of St Paul to the Romans:

“Everyone moved by the Spirit is a son of God. The spirit you received is not the spirit of slaves bringing fear into your lives again; it is the spirit of sons, and it makes us cry out, ‘Abba, Father!’ The Spirit himself and our spirit bear united witness that we are children of God. And if we are children we are heirs as well: heirs of God and co-heirs with Christ, sharing his sufferings so as to share his glory.”

Fr Matthew Boland, OP is the Master of Students, assigned to St Dominic's Priory, Melbourne.