Holy, holy, holy! Lord God Almighty!All Thy works shall praise Thy Name, in earth, and sky, and sea;Holy, holy, holy; merciful and mighty!God in three Persons, blessèd Trinity! - Reginald Heber Holy Trinity SundayOn Sunday, June 15, the church commemorates the Holy Trinity. Belief in the Holy Trinity is foundational to Christianity, and it is in the name of the Holy Trinity that every Christian is baptized.