In their popular college text Christian Foundations, husband and wife team Kathleen Fischer and Thomas Hart set aside lots of space for the Trinity.
They begin by going back to Karl Rahner's difficulty with the English word "person." The late theologian was convinced it originally didn't describe "an independent center of consciousness and freedom." "Rahner suggested 'a way of being' as a better translation . . . . The one God has three ways of being."
Rahner always contended that ". . . Trinitarian thinking began not as a piece of speculation about God, but as the expression of the religious experiences of the followers of Jesus. They experienced God in an incarnate or historically concrete way in Jesus, and they experienced God in a spiritual way in the depth of their own spirit. They called the first experience the 'Son' and the other the 'Holy Spirit.' The mystery that remains ever in the background, the mystery to which Son and Spirit pointed, they called the 'Father,' as Jesus did."
Fischer and Hart zero in on the real meaning of today's feast. When we hear the dogma of "three persons in one God," we forget that God didn't appear to the participants of the 325 CE Council of Nicea and proclaim this precise formula. That concept had been fermenting in the consciousness of Christians for almost 300 years. They hadn't read those words in a catechism and repeated them on the council floor. They simply had experienced God working in their lives on those three different levels.
We who are biblically oriented know this experience of the divine was highlighted during Moses' encounter with Yahweh on Mt. Sinai. "Having come down in a cloud, Yahweh stood there with him and proclaimed his name, 'Yahweh.' Thus Yahweh passed before him and cried out, 'Yahweh, Yahweh, a merciful and gracious God, slow to anger and rich in kindness and fidelity.'" The Chosen People will only discover Yahweh's personality by overcoming their own "still-necked" personalities long enough to permit this gracious God to be part of their "company."
Jesus' earliest disciples also struggled to express their Yahweh experiences. But no matter how they reflected on God, they always returned to their relationship with Jesus; his love of them demonstrated God's love of them. So it makes perfect sense for John's Jesus to inform Nicodemus, "Yes, God so loved the word that he gave his only Son, that whoever believes in him may not die but may have eternal life."
Fischer and Hart also refer to American theologian Catherine Moury LaCunga's insight into the Trinity. "The doctrine of the Trinitarian persons tells us that God's being is by nature relational . . . . The image of God in humanity is therefore not found in the solitary self, but in persons who are in authentic communion with others. The Trinity serves as a model for human relationships."
It's no accident that Paul mentions Jesus, God and the Holy Spirit in this specific part of II Corinthians. He's concerned that members of the community relate to one another. "Encourage one another. Live in harmony and peace, and the God of love and peace will be with you. Greet one another with a holy kiss . . . . The grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all."
It makes sense why Paul mentions God's three ways of being in the context of community relations. Only those who give themselves over to others will understand God's giving of God's self to us. The rest might have to invest in a catechism and start memorizing theological formulas.