A cynic might suggest that Christmas was simply an adaptation of the Roman festival of Saturnalia, which was popularised when Christianity became the official religion of Rome and that the story of Jesus, rather than a historical, was event was a reinvention of a much older myth.
When someone like Alasdair HB Fyfe repeats the usual superstition about the Incarnation, it is only fair that someone like me points out that Jesus himself never claimed divinity – in fact Jewish beliefs about Yahweh would have prevented even the idea. It was his followers who later turned him into a universal saviour god to rival Mithras, the popular divinity of the time.
So Jesus was not God, nor should anyone believe the stories surrounding his birth. They were invented (separately) by Matthew and Luke in an attempt to show either that his appearance was foreshadowed in the Jewish scriptures, or that he was at least as worthy of divinity as Mithras – whose birthday incidentally was 25 December.