Holy Trinity Sunday is a Christian feast that celebrates and honors the Holy Trinity. We commemorate and celebrate God who is three in one: God the Father, Jesus Christ the Son, and the Holy Spirit, that is the spirit of God. All are separate entities upon themselves, but they are also one and the same. Holy Trinity Sunday falls on the first Sunday after Pentecost, while the Trinity season begins on the Sunday after Pentecost and lasts for approximately 25 Sundays until the last Sunday before Advent in November.
During the many festivals in winter and spring, we celebrate events that are related to God the Creator, God the Son, or God the Holy Spirit. On Holy Trinity Sunday we celebrate not an event but a reality: God three in one, a unity. It is also the only Sunday in the church year dedicated entirely to God as a whole rather than the Father, Jesus, or the Holy Spirit.
Holy Trinity Sunday was officially instituted in the 9th century by Pope Gregory IX, but it had been celebrated as a tradition for hundreds of years before 828 CE, as evidenced by the adoption of the Trinitarian baptismal formula in early liturgies. However, most of the early celebrations of this holiday were done by individual churches and dioceses, and it wasn’t celebrated with a widely adopted feast. That changed in 1334 when Pope John XXII established it as a feast day.
“There is one body and one Spirit, just as you were called to one hope when you were called; one Lord, one faith, one baptism; one God and Father of all, who is over all and through all and in all.” (Ephesians 4:4-6)