Christmas is a celebration of the birth of Jesus Christ
Born nearly two thousand years ago, Christians believe Him to be the Son of God. Whether Jesus was really born on December 25th, no one can say for certain. It was chosen because it already was a holiday in ancient times -a pagan feast. But pagans did not believe in Jesus. Around the third century there was an attempt to fix the day of His birth by tying it to a festival of the Nativity kept in Rome in the time of Bishop Telesphorus (between A.D. 127 and 139). Some Christmas observances of the Roman Church are said to be of Bishop Telesphorus' appointment. There was also a story of Christians being massacred in the catacombs on the day of the Nativity between A.D. 161 and 180 but the exact year, again is not known. In A.D. 300, a similar event is said to have taken place at Nicomedia in the reign of Diocletian. Neither of these stories seem reliable as a measure of the day Christ was born.
It was believed the Nativity took place, indeed, on the 25th of the month; but which month was uncertain and every month at one time or another has been assigned. During the time of Clement of Alexandria (before 220) five dates in three different months of the Egyptian year were said to be the Nativity. One of those corresponds to the December 25th date. During the third century, it was a common belief that Christ was born on the winter solstice based on an interpetation of some prophetic scriptures and an idea that the Annunciation and the Crucifixion both occured on the same day - March 25th. Another third century set of writings, The Apostolic Constitutions, indicate the Apostles ordained that the feast be kept on the 25th day of the ninth month which, at that time meant December. The works of John Selden, published in 1661, suggested that in the early Christian ages the winter solstice fell on the 8th of the Kalends of January, that is, December 25th, though not accepted universally by modern day students who put the day between the end of July and the end of October.
The Roman Church finally fixed December 25th as the birthday of Jesus Christ after the great persecution that took place around A.D. 310; which connects the visitation of the wise men from the East, being celebrated twelve days later. Though questioned for several generations by the Eastern Church, the Roman day became universal in the fifth century.