To understand the origins of the feast of Christmas, and why its date is December 25th, one needs to know something about the origins of the feast of Epiphany, always celebrated some days after Christmas. Epiphany was celebrated by Christians before there was a Christmas. The word epiphany means revelation, manifestation, or unveiling, and this ancient feast celebrated a number of events, such as the incarnation, the birth of Jesus (which would later have its own day called Christmas), the adoration by the wise men, Jesus’ baptism by John, and the miracle at Cana. Each of these biblical events, in some way, “revealed” who Jesus was.
At its origins, the date for this feast seems to have been January 6th, most likely chosen as a counter-feast to a number of pagan festivals celebrated at that time of the year. For example, at Alexandria in Egypt, Petra in Arabia, Alusa in Palestine, and in other places, the birth of a pagan god from a virgin mother was being celebrated. In Egypt people were celebrating the rise of the Nile river that would provide irrigation, and in Greece people were celebrating the birth of the god Dionysos, which also involved springs of water that produced wine on his feast. Thus we can begin to see why Christians might choose this time of the year to celebrate the birth of Jesus, as well as other events that involved water, like the baptism of Jesus and the marriage feast at Cana. The water connections would make Epiphany an ideal day, other than Easter and Pentecost, to celebrate Christian baptism.
Eventually Christians in various places wanted to celebrate the birth of Jesus on a separate day. Not all the reasons for this are known, and what is rather certain is likewise rather complex. One reason is that Christians became very concerned about the doctrine of the nature of Christ. For instance, some Christians were mistakenly believing and teaching that Jesus was not divine from his birth, but became divine only at his baptism, when a voice from heaven was heard to say, “This is my beloved Son; listen to him.” To correct this notion, and to reaffirm the traditional teaching that Christ was divine from birth, Christian leaders thought it would be helpful to devote a particular day exclusively to the birth of Jesus.
The best that our historical evidence can tell us is that at least by the year 336 Christmas was being celebrated in Rome. Why was December 25th chosen? It was not because people believed that Jesus was born on that day, for like us, no one knew the exact date of the Lord’s birth. Once again, Christians most likely picked the 25th because pagans were celebrating something important on that day. The Romans were celebrating their worship of the sun at this precise time of the year. The dark, short days of winter were giving way to days of more light. Light was victorious over darkness, and December 25, on or about what we call the winter solstice, was a good day to celebrate the rebirth of light. For the Christians it was an equally appropriate time to celebrate Christ, the light of the world, whose coming to us overcomes sin and darkness. Even today Christmas remains a feast of light, and the Christmas lights that decorate our streets and homes and trees remain a reminder to us of Christ, victorious over all darkness.