The word Advent is from the Latin adventus for “coming” and is associated with the four weeks of preparation for Christmas. Advent always contains four Sundays, beginning on the Sunday nearest the feast of St. Andrew the Apostle (November 30) and continuing until December 24.
In 2021, Advent begins on November 28 and ends on December 24 (Christmas Eve), as the Mass of the Lord’s Nativity begins. Christmas Day is December 25.
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 to the anniversary of Our Lord’s birth on Christmas. From the earliest days of the Church, people have been fascinated by Jesus’ promise to come back. But the scripture readings during Advent tell us not to waste our time with predictions. Advent is not about speculation. Our Advent readings call us to be alert and ready, not weighted down and distracted by the cares of this world (Lk 21:34-36). Like Lent, the liturgical color for Advent is purple since both are seasons that prepare us for great feast days. Advent also includes an element of penance in the sense of preparing, quieting, and disciplining our hearts for the full joy of Christmas.
As we prepare for Christmas, the General Instruction of the Roman Missal notes some differences to the Mass that should be observed during the season. For instance, the priest will wear violet or purple during Advent, except for the Third Sunday of Advent (Gaudete Sunday) when rose is worn (GIRM, no. 316). Aside from what the priest wears, other aesthetic changes in the Church can include a more modestly decorated altar.
The final days of Advent, from December 17 to December 24, we focus on our preparation for the celebrations of the Nativity of our Lord at Christmas. In particular, the “O” Antiphons are sung during this period and have been by the Church since at least the eighth century. They are a magnificent theology that uses ancient biblical imagery drawn from the messianic hopes of the Old Testament to proclaim the coming of Christ as the fulfillment not only of Old Testament hopes, but of present ones as well.