The Missal describes the Feast Day of the birth of Christ:

During Christmastide, the liturgy shows us the Messias as the Son of God, clothed with humanity, glorified by the humble surprised shepherds, and adored by the Magi from the East. Let us fall down before the Child and bless God, for the birth of Jesus is the beginning of our Redemption through grace to the supernatural life.

Christmas is the only day of the year other than Easter which keeps the old custom of celebrating its Feast at midnight. At this hour we are called to mind that Mary in her spotless virginity gave to the world its Saviour. In the midst of darkness, the Light was born. Therefore the Church celebrates Christmas on December 25, the time of the year when the days begin to lengthen.

The custom of having three Masses originated in Jerusalem. A Mass was…