Beginning the Church's liturgical year, Advent (from, "ad-venire" in Latin or "to come to") is the season encompassing the four Sundays (and weekdays) leading up to the celebration of Christmas.
The Advent season is a time of preparation that directs our hearts and minds to Christ’s second coming at the end of time and also to the anniversary of the Lord’s birth on Christmas. The final days of Advent, from December 17 to December 24, focus particularly on our preparation for the celebrations of the Nativity of our Lord (Christmas).
Traditionally, Advent wreaths are constructed of a circle of evergreen branches into which four candles are inserted, representing the four weeks of Advent. Ideally, three candles are purple and one is rose, but white candles can also be used.
The purple candles in particular symbolize the prayer, penance, and preparatory sacrifices and goods works undertaken at this time. The rose candle is lit on the third Sunday, Gaudete Sunday, when the priest also wears rose vestments at Mass; Gaudete Sunday is the Sunday of rejoicing, because the faithful have arrived at the midpoint of Advent, when their preparation is now half over and they are close to Christmas.
The progressive lighting of the candles symbolizes the expectation and hope surrounding our Lord’s first coming into the world and the anticipation of his second coming to judge the living and the dead.