It is the beginning of a long season that takes us all the way through the rest of the liturgical year until we reach Advent.
In traditional Methodist usage, The Book of Worship for Church and Home (1965) provides the following Collects for Trinity Sunday:
Almighty and everlasting God, who hast given unto us thy servants grace, by the confession of a true faith, to acknowledge the glory of the eternal Trinity, and in the power of the divine majesty to worship the unity: We beseech thee to keep us steadfast in this faith and evermore defend us from all adversities who livest and reignest, one God, world without end. Amen.
Almighty and everlasting God, who hast revealed thyself as Father, Son, and Holy Spirit, and dost ever live and reign in the perfect unity of love: Grant that we may always hold firmly and joyfully to this faith, and, living in praise of thy divine majesty, may finally be one in thee; who art three persons in one God, world without end. Amen.