In the Cistercian liturgy the center piece of First Vespers of the First Sunday of Advent is Missus est Gabriel Angelus, a magnificent Great Responsory in the seventh mode. It places all of Advent under the sign of the Virgin who conceives and brings forth a Son.
The angel Gabriel was sent to Mary, a virgin espoused to Joseph,
to bring unto her the word of the Lord:
and when the Virgin saw the light she was afraid.
Fear not, Mary, for thou hast found grace with the Lord.
Behold, thou shalt conceive and bring forth a son,
and He shall be called the Son of the Highest.
V. The Lord God shall give unto Him the throne of His father David,
and He shall reign over the house of Jacob forever.