Trinity Sunday is the first Sunday after Pentecost. Trinity Sunday celebrates the Christian doctrine of the Trinity, the three Persons of God: the Father, the Son, and the Holy Spirit. Though this holy day is not recognized by all Christians, the Pentecost was a monumental turning point in Christian history, considered by many to be the birthday of the church and is a watershed event in Christianity.
While the word “trinity” does not appear in Scripture, it is taught in Matthew 28:18-20 and 2 Corinthians 13:14 along with many other Bible passages. Understanding this comes through the work of the Holy Spirit; therefore, it is appropriate that this mystery is celebrated the first Sunday after Pentecost, when the outpouring of the Holy Spirit first occurred.
Thomas Becket (1118–70) was consecrated Archbishop of Canterbury on the Sunday after Pentecost (Whitsun), and his first act was to ordain that the day of his consecration should be held as a new festival in honor of the Holy Trinity. This observance spread from Canterbury throughout the whole of western Christendom.
The Athanasian Creed, although not often used, is recited in certain Anglican churches, particularly those of High Church tendency. Its use is prescribed in the 1662 Book of Common Prayer of the Church of England for use on certain Sundays at Morning Prayer, including Trinity Sunday, and it is found in many modern Anglican prayer books. It is in the Historical Documents section of the 1979 Book of Common Prayer (Episcopal Church), but its use is not specifically provided for in the rubrics of that prayer book.
Trinity Sunday has the status of a Principal Feast, and is one of seven principal feast days, in the Episcopal Church.