The United States is a secular nation. Period.

[Still Blue in PDX]

27. Not to cause a resurgence of the (theoretical) war on Christmas, but . . .

Why Christmas carols make the church feel nervous
Some Christmas songs have origins that go back to pagan times.

Christmas wouldn’t be Christmas without the sound of carols, but we often forget that in centuries past it made the Christian church feel slightly uncomfortable. In the early thirteenth century, St Francis wrote some hymns on the theme of the nativity which were decorously sung as part of the liturgy, but the more rumbustious musical celebration of Christmas has always taken place as much outside church as inside it.

Many of the oldest examples, for example, the anonymous The Holly and the Ivy, The Twelve Days of Christmas or the Boar’s Head Carol, probably have pagan origins in ritual fertility dances and singing games which the more puritanical wing of the Reformation did not approve of. Oliver Cromwell went so far as to ban carol singing during the latter years of the Commonwealth, although this proved about as effective as Labour’s hunting ban, and was swiftly rescinded.

http://www.telegraph.co.uk/topics/christmas/6827563/Why-Christmas-carols-make-the-church-feel-nervous.html