“…So they can’t challenge my sov’reignty”?
I have a set of Christmas CDs which inexplicably contains “The Bells of (clong) St Mary’s (clong)”. While the song involves church bells, there is no mention of anything religious beyond the hint of a church wedding in the future. None of the secular trappings of Christmas are mentioned. The only line that mentions anything that can be associated with a season is “when red leaves are falling”, which happens months before Christmas. But it’s on a Christmas CD.
I set my mother to puzzling this out once - she’s my go-to source of information on American movie musicals from the 1940s and '50s, because she remembers everything about them. All she could come up with was that in the movie of the same name, the kids put on a Christmas pageant. That’s it. That’s the entire connection to Christmas.
Said the king to the people everywhere
Listen to what I say (listen to what I say)
A child, a child could make my kingdom fall
So go forth and slaughter them all
So go forth and slaughter them all
And Bilbo: that one line is why. Lewie is somewhat baffled by its adoption as a Christmas song too.
The Power of Love, by Frankie Goes To Hollywood. That one gets regular airtime over here during December. I don’t know why either, but I don’t mind much. I love it.
Sounds like your mom has it, for the most part. The Wikipedia entry on the the movie says:
I don’t get it either. Another song that I have never thought is really about Christmas is “Hard Candy Christmas” when the song sounds like that it is more about a person not letting a difficult day get them down.
God bless you always!!! 
Holly