Trinity Sunday is the feast day celebrating the Trinity. A feast is an observance commemorating a person or thing (or God). Easter is feast day, for example, and many saints have feasts. On the church calendar, Trinity Sunday always comes on the first Sunday after the Day of Pentecost.
As any priest preaching this Sunday can tell you, the Trinity is difficult to explain. The collect and preface in The Book of Common Prayer for Trinity Sunday—prayers specific to the day—invite us to contemplate the three-fold nature of God: manifested as the Father, Son, and Holy Spirit, and yet one unified Being:
For with your co-eternal Son and Holy Spirit, you are one God, one Lord, in Trinity of Persons and in Unity of Being; and we celebrate the one and equal glory of you, O Father, and of the Son, and of the Holy Spirit. - The Book of Common Prayer, page 380
Trying to explain the Trinity has led theologians to concepts such as hypostases (which means three consubstantial persons) and homoousios (substance, essence, or nature). In somewhat simpler terms, Roman Catholics have been taught over the centuries that St. Patrick used a shamrock to visualize the mystery of the Trinity, how a single plant with three leaves is analogous to the one triune God with three separate and distinct persons. We’ll delve deeper into the theology of the Trinity in a future Episcopal Explained.
Trinity Sunday is often associated with Thomas Becket, an Archbishop of Canterbury in the twelfth century, who was consecrated bishop on the Sunday after Pentecost. But it is also believed to have been celebrated with a mass created by St. Alcuin in the eighth century. Becket celebrated the feast at Canterbury and later Pope John XXII made it an official observance of the Catholic Church in 1334.
It is also a special day at Trinity Church, because it is the patronal feast day of the church, meaning the feast of the patron saint or title of the church. There will be a parish picnic on Sunday in observance of the day.
Homepage photo: icon by medieval painter, Andrej Rublëv.