If someone were truly “in his service” they would recognize that Matthew, Luke, and John all begin with the incarnation of the 2nd person of the Trinity.
So, we celebrate Jesus’ conception, birth, and presentation before God.
Most of the celebration in our churches, if we were dealing with honest people, revolves around the scriptural stories of Shepherds, Angels, Wise Men, Parents, and Baby.
Get 20 children in a room under the age of 14 and ask them what Christmas is all about. Maybe on a good day one or even two of them will mention Jesus.