Christmas Day is a Holy Day of Obligation. It is the second most important feast in the liturgical year, behind Easter. Therefore, it is important for us to gather as one body and to worship Christ on this feast of His nativity.
First Sunday of Advent (November 30): A lso the feast of St. Andrew, marks the beginning of the solemn season leading up to Christmas and occurs four Sundays prior to Christmas Day. Advent actually is a time for prayer, fasting, and confession.
Christmas derives from the combination of Christ and Mass; it is the feast of the Nativity of Our Lord and Savior Jesus Christ.
Christmas was not celebrated by the earliest Christians. The custom was to celebrate a saint's birth into eternal life - in other words, his death. Thus Good Friday (Christ's death) and Easter Sunday (His Resurrection) took center stage.
To this day, the Church celebrates only three birthdays: Christmas; the Nativity of the Blessed Virgin Mary; and the Birth of John the Baptist. The common thread in the celebrations is that all three were born without sin: Christ, because he was the Son of God; Mary, because she was sanctified by God in the Immaculate Conception; and John the Baptist, because his leap in the womb of his mother, Elizabeth, at the Visitation is seen as a type of Baptism.
It took a while for the Church to develop the feast of Christmas. While it may have been celebrated in Egypt as early as the third century, it did not spread throughout the Christian world until the middle of the fourth century. It was first celebrated along with Epiphany, on January 6; but slowly Christmas was separated out into its own feast, on December 25. Many of the early Church fathers regarded this as the actual date of Christ's birth, though it does coincide with the Roman festival of Natalis Invicti (the winter solstice, which the Romans celebrated on December 25), and the Catholic Encyclopedia does not reject the possibility that the date was chosen as "a deliberate and legitimate 'baptism' of a pagan feast."
By the middle of the sixth century, Christians had begun to observe Advent, the season of preparation for Christmas, with fasting; and the 12 days of Christmas, from Christmas to Epiphany, had become established.