Advent

"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 Saviour's first coming, the faithful renew their ardent desire for his second coming. 200 By celebrating the precursor's birth and martyrdom, the Church unites herself to his desire: "He must increase, but I must decrease.""

 Catechism of the Catholic Church 524