The Feast of the Holy Trinity was instituted by Bishop Stephen of Liége (850-920), enjoined by Pope John XXII in 1334, and became very popular in England, no doubt because of its association with the consecration of St Thomas a Becket on that date in 1162.
As the plants of the earth grow and flourish in the brightness of the Summer sun and season, may we grow in God's grace throughout the season of Trinity, bathed in the light of the teachings of the Son of God, Jesus Christ our Lord.
To aid in your personal preparation for attending the day's mass, the Trinity Sunday propers (Collect, Epistle & Gospel) are posted HERE.