One of the songs we sang in church on Christmas was one of my favorites. I have several favorites. I noted that the footnote on the hymn was from a book of carols from the 1800s that I had never heard of. I wrote down the citation and went home to see if I could order a copy of it. I collect hymnals, don't ask me why.
To my delight, I discovered the entire hymnal is found online here. It is worth looking at, if for no other reason that to see the artwork depicted.
For Christmas liturgy nerds like myself, I also discovered this little website called HymnsandcarolsofChristmas.com that has a wealth of information about the various Christmas carols. It is worth perusing.
One of the reasons I like studying carols is that many times, so much of the lesson from the carol itself is lost. I mean, we can sing so many of the first verses of classic Christmas carols, but, for instance, do you really know why we sing about Good King Wencelas? You have to read the entire hymn text to understand it.
And there are so many good carols that just have almost been lost to the time, because we don't sing them anymore.