As Fr. John Hardon points out in his Modern Catholic Dictionary, the origins of the celebration of Trinity Sunday goes all they way back to the Arian heresy of the fourth century, when Arius denied the divinity of Christ by denying that there are three Persons in God. To stress the doctrine of the Trinity, the Fathers of the Church composed prayers and hymns that were recited on Sundays as part of the Divine Office, the official prayer of the Church. Eventually, a special version of this office began to be celebrated on the Sunday after Pentecost, and the Church in England, at the request of St. Thomas à Becket (1118-1170), was granted permission to celebrate Trinity Sunday. The celebration of Trinity Sunday was made universal by Pope John XXII (1316-34).
For many centuries, the Athanasian Creed was recited at Mass on Trinity Sunday. While seldom read today, the creed can be read privately or recited with your family to revive this ancient tradition.
