For many (maybe most) of us, the Trinity has always seemed somewhat abstract – a doctrine duly believed in, of course, but not something otherwise given a lot of thought.
I say this, despite the obvious fact that we were all baptized in the name of the Father, and the Son, and the Holy Spirit. On that occasion, we – or our parents and godparents - all made a profession of faith in the Father, and the Son, and the Holy Spirit. Our sins have been forgiven in the sacrament of Penance, in the name of the Father, and of the Son, and of the Holy Spirit. Those of us who are married have exchanged wedding rings in the name of the Father, and of the Son, and of the Holy Spirit. We have all been blessed in the name of the Father, and of the Son, and of the Holy Spirit. The principal prayers of the Mass are all explicitly addressed to the Father, through the Son, in the unity of the Holy Spirit. In short, our entire religious lives, both individually and as a Church community, have been defined, formed, shaped by the awesome mystery of who God is, that defines the Triune God’s relationship with us and ours with God.
Admittedly, the words we use when we speak about the Trinity, words like one “nature” and three “persons,” when used not as we use them in ordinary language, but as technical terms of philosophical language, may seem – especially perhaps to post-modern ears – to be much too abstract. For all its apparent abstraction, however, the doctrine of the Trinity is our fundamental – and uniquely Christian – insight into who God is. As human beings, created in the image and likeness of God, we have a built-in natural, longing for God. The fact that God is, that is something we can experience naturally. Who God is, however, who God is in himself, is something we most certainly could never completely come to know on our own. That had to be revealed to us. And so God himself has revealed who he is – one God in three distinct Persons: Father, Son, and Holy Spirit.
We do not worship three gods, but one God – a unity of Persons in one divine nature or substance. Each of the three Persons, Father, Son, and Holy Spirit, is truly God, each distinctly God, but in relationship to each other, that is to say, what is distinct about each Person is his relationship to each of the others: the Father to the Son, the Son to the Father, and the Holy Spirit to both.
On the one hand, the doctrine of the Trinity expresses our uniquely Christian insight into the inner life of God, what today's Preface calls "a Trinity of one substance" – 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 Moses testified in today’s 1st reading [Deuteronomy 4:32-34, 39-40] - as one who reveals himself in how he acts toward us.
It is, of course, the Son, consubstantial with the Father, who, for our salvation, came down from heaven. 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 is inseparable from the Father and the Son, in both the inner life of the Trinity and his gift of love for the world. Led by the Holy Spirit, St. Paul tells us, we become true sons and daughters of God the Father and joint heirs with Christ [Romans 8:14-17].
The Holy Spirit unites us with the Father in the Body of Christ, the Church. Through the sacraments, Christ continues to communicate the Holy Spirit to the members of his Church. Thus, in the Eucharistic Prayer, at the very heart of the Mass, the Church petitions the Father to send the Holy Spirit, so that bread and wine may become the body and blood of Christ and that those who receive Christ’s body and blood may then be transformed into the image of Christ as participants in the mission of the Church.
Hence, the Church faithfully and gratefully prays: in the name of the Father and of the Son and of the Holy Spirit.
Homily for Trinity Sunday, Immaculate Conception Church, Knoxville, TN, June 3, 2012.