The following is taken from churchyear.net...
The word "advent," from the Latin adventus (Greek parousia), means "coming" or "arrival" and the season of Advent is focused on the "coming" of Jesus as Messiah (Christ or King). Our worship, scripture readings, and prayers not only prepare us spiritually for Christmas (his first coming), but also for his eventual second coming. This is why the Scripture readings during Advent include both Old Testament passages related to the expected Messiah, and New Testament passages concerning Jesus' second coming as judge of all people. Also, passages about John the Baptist, the precursor who prepared the way for the Messiah, are read. All of these themes are present in Catholic worship during Advent, which The Catechism succinctly describes:
When the Church celebrates the liturgy of Advent each year, she makes present this ancient expectancy of the Messiah, for by sharing in the long preparation for the Savior's first coming, the faithful renew their ardent desire for his second coming. By celebrating the precursor's birth and martyrdom, the Church unites herself to his desire: "He must increase, but I must decrease" (524).
