I've long been interested in hymns and their stories. I have multiple iterations of those hymn-story books, and love reading about the origins and meanings of some of the hymns therein. I especially enjoy reading about songs that are more than two hundred years old.
As Christmas season approaches, it isn't too hard to see that there is really little theology left in the holiday. It has become secularized and commercialized (more of the latter, which results in the former, I think). The last vestige of any theology outside church services is found in some of the Christmas music that has remained popular in spite of their lyrics. Here's an example- I have XM/Sirius satellite radio in a couple of my vehicles, and I tune in to the couple of seasonal stations that they put up during the holidays. One, called Holly, is really about as secular as it can get, and is new music, so I don't listen much. The other, called Holiday Traditions, is more older stuff that we heard when I was a kid. (But note, there is no Xmas hint in the station's title.) The Holiday Traditions station plays a lot of secular seasonal music, but occasionally slips in a religious Christmas song, if it was performed by one of the greats (Crosby, Martin, Presley, etc.). I heard Hark! The Herald Angels Sing yesterday. Have you ever paid attention to the lyrics to that song? The gospel is in there, and it can't be confused with any moralistic therapeutic deism, much less secular winter solstice worship.
Pete Scribner, over on his Sola Gratia blog (which I both follow and recommend), has just posted a couple of really neat posts about the song O Come, O Come Emmanuel.
The first post of the pair is here, and the second is here.
He talks about several aspects of this song, but also about how the real Christmas music works year-round, because it isn't oriented toward a holiday, but toward the gospel, at least the part of the gospel that is the incarnation of Christ. I don't think the gospel orientation is why the songs have become traditions...if anything, the wording is offensive to secular culture and in many cases the lyrics get changed to fit the artist's taste (heard Have Yourself a Merry Little Christmas lately? It's not even a religious song, but the line, ...if the Lord allows has been changed to, ...if the fates allow. And they say Calvinists are fatalists...). I think R. C. Sproul got it right, in the video of the Q and A time at one of the Ligonier national conferences, when he points out that the high church music lasts because it is complex and strives to glorify God rather than be simple to perform; that's why the music has become a landmark.
But enough analysis. Give these posts a read...they are worth the time taken as a devotional this time of year.