The festivals associated with celebrating the winter solstice in the more northern places were easily adapted by the Christian philosophers. But the essence of something like Christmas remains essentially Pre-Christian and the thing of it is why isn't the day of Christmas on December 21st?
There could well have been some kind of calendar issue, an error in translation
following a calendar upgrade, easily done, but more likely it was a deliberate
contrivance on the part of the faithful to isolate the birth of the Christian
Prophet from the multitude. It was The Puritans who had it right, they tried to
ban Christmas and had they succeeded more likely we would be celebrating
Christmas on December 21st.