Abrahamic / Middle Eastern Christianity What Is Trinity Sunday? Share Flipboard Email Print Illustration of the Hospitality of Abraham. Fine Art Images / Getty Images Christianity Catholicism Holy Days and Holidays Beliefs and Teachings Prayers Tips Worship Saints Christianity Origins The Bible The New Testament The Old Testament Practical Tools for Christians Christian Life For Teens Christian Prayers Weddings Inspirational Bible Devotions Denominations of Christianity Funerals and Memorial Services Christian Holidays Christian Entertainment Key Terms in Christianity Latter Day Saints View More By Scott P. Richert Catholicism Expert M.A., Political Theory, Catholic University of America B.A., Political Theory, Michigan State University Scott P. Richert is senior content network manager of Our Sunday Visitor. He has written about Catholicism for outlets including Humanitas and Catholic Answers Magazine. our editorial process Scott P. Richert Updated May 07, 2019 Trinity Sunday is a moveable feast celebrated a week after Pentecost Sunday. Also known as Holy Trinity Sunday, Trinity Sunday honors the most fundamental of Christian beliefs—belief in the Holy Trinity. The human mind can never fully understand the mystery of the Trinity, but we can sum it up in the following formula: God is three Persons in one Nature. There is only one God, and the three Persons of God—the Father, the Son, and the Holy Spirit—are all equally God, and They cannot be divided. Quick Facts Date: The Sunday after Pentecost Sunday.Type of Feast: Solemnity.Readings (Year A): Exodus 34:4B-6, 8-9; Daniel 3:52, 53, 54, 55, 56; 2 Corinthians 13:11-13; John 3:16-18Readings (Year B): Deuteronomy 4:32-34, 39-40; Psalm 33:4-5, 6-9, 18-19, 20-22; Romans 8:14-17; Matthew 28:16-20Readings (Year C): Proverbs 8:22-31; Psalm 8:4-5, 6-7, 8-9; Romans 5:1-5; John 16:12-15Prayers: The Sign of the Cross; The Glory Be; The Athanasian CreedOther Names for the Feast: The Solemnity of the Most Holy Trinity, Holy Trinity Sunday History As Fr. John Hardon points out in his Modern Catholic Dictionary, the origins of the celebration of Trinity Sunday go all the way back to the Arian heresy of the fourth century. Arius, a Catholic priest, believed that Jesus Christ was a created being rather than God. In denying the divinity of Christ, Arius denied that there are three Persons in God. Arius' chief opponent, Athanasius, upheld the orthodox doctrine that there are three Persons in one God, and the orthodox view prevailed at the Council of Nicaea, from which we get the Nicene Creed, recited in most Christian churches every Sunday. (The Council of Nicaea also gives us a wonderful example of how a real bishop deals with a heretic: Confronted with Arius' blasphemous views, Saint Nicholas of Myra—the man best known today as Santa Claus—marched across the council floor and slapped Arius across the face. To stress the doctrine of the Trinity, other Fathers of the Church, such as St. Ephrem the Syrian, composed prayers and hymns that were recited in the Church's liturgies and 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 (1118-70), was granted permission to celebrate Trinity Sunday. The celebration of Trinity Sunday was extended to the entire Church by Pope John XXII (1316-34). For many centuries, the Athanasian Creed, traditionally ascribed to Saint Athanasius, was recited at Mass on Trinity Sunday. While seldom read today, this beautiful and theologically rich exposition of the doctrine of the Holy Trinity can be read privately or recited with your family on Trinity Sunday to revive this ancient tradition.