There are so things that we know about the birth of Jesus; there are also some things that we definitely do not know. All we really know for sure is what we find in the Bible. We know, for example, that Jesus was born of the virgin, Mary. (Matthew 1:22-23; Luke 1:34-35) But we know nothing of the Immaculate Conception, Perpetual Virginity, Assumption or Veneration of the virgin Mary. The Bible says nothing about these; they are all human traditions with no basis in fact.
We know that Jesus was born in the reign of Caesar Augustus. (Luke 2:1ff) But we do not know the date of His birth. December 25 is merely a human tradition and not found in the Bible. Nor do we know of any special day for the celebration of the birth of Jesus. No such holy day can be found in the Bible.
While it is fine to enjoy a festive season, we should not be misled into thinking that God authorized a certain day for a special celebration of the birth of Christ.