This Sunday, the Third Sunday of Advent, is known as Gaudete Sunday, which is taken from the entrance antiphon since it begins with "Rejoice..", or "Gaudete" in Latin. We also begin to sing "O Come, O Come Emmanuel" this week since the chorus is based on this entrance antiphon, and the verses are based on the O Antiphons. The O Antiphons, which are a series of antiphons for the last seven days of Advent (typically sung at Vespers), usually begin during the 3rd week in Advent.
Rejoice in the Lord always; again I say, rejoice. Indeed, the Lord is near.
Entrance: O Come, O Come Emmanuel
Responsorial Psalm: Luke 1 My Soul Rejoices in My God
Offertory: Holy (Jesus, You Are)
Say to the faint of heart: Be strong and do not fear. Behold, our God will come, and he will save us.
Communion: Rorate Caeli Desuper
Communion: I Will Exalt You
Recessional: Great Things