Let us start off with the origin of the word
Christmas:
"The word for
Christmas in late Old English is
Cristes Maesse, the Mass of Christ, first found
in 1038, and Cristes-messe, in 1131"
- Christmas, Catholic Encyclopedia
(http://www.newadvent.org/cathen/03724b.htm)
The word "Christmas" is just a
contraction of "Christ's Mass" or "Mass of Christ", which was a
special Catholic Mass
to celebrate Christ's birth.
I wonder if Christmas Eve communion services
in protestant
churches today also stem from this practice?