The bible does not mention any sort of celebration for
Jesus, the apostles and the early church did not celebrate
His birth either.
After the 3rd century, Christians started taking part in
blatant pagan sun worship celebrations.
The Church leaders tried as hard as they could, but they
could not stop the influence
and the spread of these
pagan celebrations within Christianity
Getting tired of constantly fighting against them, they
decided to "Christianize" these pagan celebrations and
allow them to continue as “Christian” celebrations
In the 4th century, the Church at Rome declared
December 25th (a well established pagan holiday) as the
official birthday of Christ.