The third Sunday of Advent, so called from the first word of the Introit at Mass (Gaudete, i.e. Rejoice). The 3rd candle in the Advent wreath is called the “Shepard's Candle,” and is rose is a liturgical color for joy.
1. Advent still preserved most of the characteristics of a penitential season which made it a kind of counterpart to Lent, the middle (or third) Sunday corresponding with Laetare or Mid-Lent Sunday. On it, as on Laetare Sunday, flowers, forbidden during the rest of the season, were, permitted to be used; rose-coloured (not pink) vestments were allowed instead of purple (or black, as formerly).
2. Gaudete Sunday, therefore, makes a breaker like Laetare Sunday, about midway through a season which is otherwise of a penitential character, and signifies the nearness of the Lord's coming.
3. In both Office and Mass throughout Advent continual reference is made to our Lord's second coming, and this is emphasized on the third Sunday by the additional signs of gladness permitted on that day.
4. Gaudete Sunday is further marked by a new Invitatory, the Church no longer inviting the faithful to adore merely "The Lord who is to come", but calling upon them to worship and hail with joy "The Lord who is now nigh and close at hand". The joy of expectation is emphasized by the constant Alleluias, which occur in both Office and Mass throughout the entire season.
5. 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.
Edited from the Catholic Encyclopedia
PRAYER for Gaudete Sunday :
Dear God, you know that our hearts long for the joy and gladness promised by life with you. Help us to remember that you are with us always, and that our hearts will rest only when they rest with you. » Holy Spirit, guide the choices we make throughout this week. Help us endure hardship. Remind us to be patient. Stifle our tendency to complain. Help us realize how much we owe the creator for all we have and all we are. » Father in heaven, we offer thanks to you for sending John the Baptist to prepare the way for the coming of the savior. Help us to heed the Baptist’s message to repent and to renew our commitment to live in holiness. » Come Lord Jesus. So often we are impatient for your coming, yet we are fearful of living our lives as one with you. Come and ease our anxiety. Come and reward our patience. Come and remove our sorrow. Our communities and our world eagerly await the day of your birth.