What we do know is that the angel announced,
“There is born this day in the city of David a Savior, who is Christ the Lord.”
The reason for Christmas, the reason we celebrate is because God became flesh to become our Savior.
We celebrate that a loving God made it possible that sinful man could have a relationship with Him through believing and receiving Jesus Christ as our Lord and Savior.
That is why we can say with a joyful heart, “Merry Christmas!”.