 I personally come from an Orthodox Christian background and very well aware with the historicity of Christmas, the pagan influence on Christmas, the changing of dates especially as well. If you look into Roman Catholicism you will see that Christmas is on the 24th to 25th of December. However in Orthodox Christianity it is on the 6th to 7th January. So there you can see already a discrepancy within the alleged date of Jesus' birth. The two churches already do not agree what the real birth date is. Moreover if you look into the 24th, the 25th you will see that this was the winter solace. So this was a holiday for the pagans of the Roman Empire and once the Roman Empire became Christian they adopted Christianity as their state religion. They simply replaced their old holidays with new ones and renamed them.