The name “Christmas” did not come into use until the Middle Ages. It is a contraction of the term “Christ’s Mass.”
In early centuries, Christians were more likely to celebrate the day of a person’s death than the person’s birthday. Very early in the life of the church, the people held an annual observance of the death of Jesus and the early martyrs on the day of their deaths.
Until around the fourth century, churches in the East observed “Epiphany.” Epiphany is the manifestation of Christ to the Gentiles as represented by the Magi. (Matthew 2:1-12.) This was a feast commemorating the birth of Christ, His baptism, and the manifestation of God to the world.
Christians in Rome began to celebrate the birth of Christ in the early part of the fourth century. This practice spread rapidly in the Christian world, so by the end of the fourth century, this new festival was observed by Christians everywhere.
The controversy over the nature of Christ led to an increased emphasis on the doctrine of the incarnation. What is incarnation? Incarnation refers to the affirmation that God, in one of the modes of His existence as a Trinity, He revealed Himself to humanity. God becoming human: the union of divinity and humanity in Jesus of Nazareth. John 1:14 the scripture says, “And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.”
The exact date of the birth of Christ is not known. Throughout the Roman Empire, festivals were celebrated in conjunction with the winter solstice. When Christianity became the religion of the Empire, the winter solstice seemed an appropriate time to celebrate the birth of Christ. The December 25 date was chosen for practical reasons as well as theological ones.
Roman Catholics and Protestants celebrate the birth of Christ on the 25th of December. As early as A.D. 326, the western churches celebrated Christmas on December 25. The Eastern Orthodox churches celebrate on January 6 and he Armenian churches celebrate on January 19.