Gaudete Sunday Rejoice!

Since the middle ages the third week of Advent is celebrated with the proclamation taken from the Latin Introit antiphon "Gaudete" based on St. Paul's letter to the Thessalonians, Rejoice always!
  Advent is considered a penitential season, like Lent. We are encouraged to take a spiritual inventory, making sure we are preparing Him room in our hearts. Most parishes provide extra opportunities for the sacrament of reconciliation and our parish has confession after every Mass. Long ago, the  faithful fasted, not feasted during advent!  So today we pass the midway point of advent and the Church gives us the opportunity to rejoice anticipating the coming of the Lord. The priest's vestments are brightly rose colored  instead of the dark purple during the other Sundays of advent. The third candle of the advent wreath lit is a bright rose distinguishing this Sunday from the others.

"The spirit of the Office and Liturgy all through Advent is one of expectation and preparation for the Christmas feast as well as for the second coming of Christ, and the penitential exercises suitable to that spirit are thus on Gaudete Sunday suspended, as were, for a while in order to symbolize that joy and gladness in the Promised Redemption which should never be absent from the heart of the faithful." (cf. NewAdvent)