According to the famous legend, Saint Patrick is said to have used a shamrock to teach the doctrine of the Trinity when evangelizing Ireland in the 5th century. The fact that Patrick had to resort to using a shamrock illustrates the challenge of talking about the Trinity.
Created in the image and likeness of God, we all have a built-in natural longing for God. So we can theorize about God’s existence by our ordinary natural reasoning process. But who God is - in himself - that is something we cannot possibly know on our own. That had to be revealed to us. So the doctrine of the Trinity is our fundamental – and uniquely Christian – insight into who God is.
On the one hand, the doctrine of the Trinity expresses our uniquely Christian insight into the inner life of God – where the Son is the image of the Father, the Father’s likeness and outward expression, who perfectly reflects his Father, while the Holy Spirit in turn expresses and reveals the mutual love of Father and Son. At the same time, the Trinity also expresses something fundamental about how God acts outside himself. Who God is in himself is how God acts. And so how God acts reveals who God is.
Already in the Old Testament, God was revealing himself – as he did to Moses in today’s 1st reading, as one who reveals himself in how he acts toward us: a merciful and gracious God, slow to anger and rich in kindness and fidelity. It was to such a God that Moses prayed – as we all pray – do come along in our company … and receive us as your own.
It is, of course, the Son, consubstantial with the Father, who, as the visible image of the invisible God, came down from heaven, so that the world might be saved through him. Risen from the dead and seated at the right hand of the Father, the Son has sent the Holy Spirit upon his Church, which is the Body of Christ and the Temple of the Holy Spirit. The Holy Spirit unites us with the Father in the Body of Christ. Through the sacraments, Christ continues to communicate the Holy Spirit to the members of his Church, so that we can become the people Saint Paul instructs us to be: Mend your ways, encourage one another, agree with one another, live in peace, and the God of love and peace will be with you.
This is what our external sharing in God’s inner life involves. Just as God’s inner life is itself a unique kind of community, so too our life as Church is a unique community in unity, a distinctive way of living, a new way of being human together.
As we survey the sad wreckage of our society and the long legacy of damage individualism has done to our ability to live as humans together in God’s company, we recognize all the more urgently how uniquely demanding and uniquely necessary is our full participation in the life of the Trinity through this new way of being that the Father, the Son, and the Holy Spirit have revealed to us and called us to share in.
As the 4th century Bishop and Doctor of the Church, St. Athanasius, famously wrote in one of his letters: “When we share in the Spirit, we possess the love of the Father, the grace of the Son, and the fellowship of the Holy Spirit himself.”
Hence, the Church faithfully follows Saint Paul in praying: The grace of our Lord Jesus Christ, and the love of God, and the communion of the Holy Spirit be with you all!
Homily for Trinity Sunday, Immaculate Conception Church, Knoxville, TN, June 7, 2020.