[topcat54]

Well that's the point; asserting that Christmas is not Christian in origin is to assert that Christians should not participate in Christmas. An inoccuous-seeming message about curiosities becomes a challenge to the piety of Christmas, if it argues that Christmas is not a Godly celebration.

Correct. If it is not sanctioned by the Word of God one cannot legitimately claim any "Christian piety" associated with its observance.

[dangus]

Well, I think Calvin overstates his case. The bible tells us very little about how or when to pray. Plainly, public prayer meetings were sanctionned (cf. I Cor 9-12), but other than Paul's guidance about what NOT to do, there's very little material provided for how they should be conducted. The crucial thing is that we not let the trappings of the holiday numb us to the wonders of the holyday.