I don't mean to keep bringing up the annotations in the version I read, but it's pertinent to this discussion -
The Christian aspect is discussed. Basically what I took is that Dickens purposefully kept religion mostly out of it. Strict religion, and the Puritans, were in his mind what were destroying the Christmas celebrations (the Puritans thought Christmas celebrations were too similar to a Pagan Roman holiday and so didn't want to celebrate it).
So he wanted to write a book celebrating the spirit of Christmas and the joy and fun and charity and warmth of it without really including religion.