Trinity Sunday is one of the four solemnities of the Lord during Ordinary Time. Since these feasts are dependent upon the celebration of Easter, they are called movable solemnities of Ordinary Time. The solemnities are: Trinity Sunday, Corpus Christi, Sacred Heart and Christ the King.
Adolf Adam calls them feasts of devotion and feasts of ideas. As feasts of devotion they are expressions of piety born in response to an internal or external trial. As feasts of ideas, each one extols a particular truth or specific aspect of the mystery of Christ. By stressing these truths or mysteries, the Church hoped to renew and strengthen the faith of God’s people.
The Arian controversies of the 4th and 5th centuries gave rise to a strong emphasis on and devotion to the Trinity in Spain and Gaul. Arius, a priest in Alexandria who died in 336, denied the divinity of Christ. As a result, faith in God, the Father, Son, and Holy Spirit and the equality of the three Divine Persons was threatened. The Councils of Nicea and Constantinople (381) condemned the heresy and formulated the Nicene Creed, the profession of faith recited at every Sunday mass.
The heresy had an impact on Catholic faith and life. Preaching sought to strengthen faith in the church’s doctrine regarding the Trinity. The first preface of the Trinity found its way into the liturgy in the 400’s as this feast was born out of controversy. The modern preface of the Trinity appeared during the eighth century. By the year 1000, the feast of the Trinity was celebrated on the Sunday after Pentecost. The feast reminds the faithful of what it means when we refer to the Father, Son, and Spirit: We believe in three Divine Persons in one God.
The Sunday assembly professes faith in the Triune God when it begins every gathering by invoking “The grace of our Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.”