Trinity Sunday appears to stand out as an oddity in the church calendar. Israel’s calendar was filled with commemorations of events in Israel’s history, and the Christian calendar is predominantly about the events of the incarnation. And then comes Trinity Sunday and Trinity season, devoted to a “doctrine” rather than an event.
I think that’s the wrong way to understand Trinity season. Rather, Trinity Sunday comes as the culmination of the redemptive-historical celebrations, as a clue to the inner meaning of those celebrations. In Advent, Christmas, Lent, Holy Week, Easter and Ascension, we celebrate the work of the Son for our redemption. At Pentecost we commemorate the gift of the Spirit to the church. Trinity tells us that these events in history unveil the inner reality, the inner life of God. Trinity Sunday reminds us that the missions of the Son and Spirit reveal the processions of the Son and Spirit (to use Augustine’s terminology). Trinity is not a departure from the redemptive-historical celebrations that precede it, but the climax of those celebrations.