Asperges Me

Asperges Me is a Latin antiphon said or sung at a Roman Catholic Solemn Mass in all seasons except the Easter (Paschal) season and Palm Sunday. It traditionally accompanies the Asperges, the ritual sprinkling of the congregation by the celebrant with holy water, as part of an entrance ritual, symbolising the cleansing of the people. Its words are taken from Psalm 51 (50):

Thou wilt sprinkle me, O Lord, with hyssop and I shall be cleansed
Thou wilt wash me, and I shall be washed whiter than snow.
Pity me, O God, according to Thy great mercy.

It is followed by the conventional doxology (except on the first Sunday of Passiontide):

Glory be to the Father, and to the Son, and to the Holy Ghost
As it was in the beginning, is now, and ever shall be, world without end. Amen.

The antiphon is then recited a second time.

From Easter until Pentecost, Asperges me is replaced by the more lengthy and florid antiphon, Vidi aquam.

Although usually sung to plainchant, Asperges Me has been set to music; two well-known examples are those by Gilles Binchois (Bologna, International museum and library of music, Ms Q15) and Tomás Luis de Victoria.

...
Wikipedia