This is the familiar salutation of the angel Gabriel in a musical setting from 12th-century Beauvais; it belongs to a longer office for the Christmas season. The text is from the Gospel according to St. Luke.
Ave Maria gratia plena, dominus tecum, virgo serena; benedicta tu in mulieribus que peperisti pacem hominibus et angelis gloriam. Et benedictus fructus ventris tui qui coheredes ut essemus sui nos fecit per gratiam.
Hail, Mary, full of grace! The Lord is with you, untroubled maiden. You are blessed among women, you who brought forth peace to men and glory to angels. Blessed, too, is the fruit of your womb, who by grace made it possible for us to be his heirs.