A Charlie Brown Christmas, CBS (reruns on ABC)
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There have been lots of Charlie Brown specials over the decades, far more than I've seen. And I've probably seen some I don't really remember at all, now. But this one was the first (originally airing in 1965), and the best. Charlie Brown is upset that he always seems to get depressed around the holidays, because of the over-commercialization of the holiday, and because not getting Christmas cards emphasizes the fact that people don't like him. (Of course, depression is pretty common during the holiday season. I'm not sure, but I doubt that fact was touched on much, at the time the special was made. So it may be a bit ahead of its time.) Charlie goes to consult Lucy at her psychiatric stand, and she says he needs involvement, so she makes him the director of the Christmas play she and the other kids (and Snoopy) are putting on. Charlie tries his best to, you know, give the play some direction, but no one pays any attention to him. Honestly, I don't think any of them cared about the play at all, since they spent all their time just dancing to the non-Christmasy music Schroeder was playing.
After awhile, Charlie Brown and Linus go out to get a Christmas tree to use in the play, hoping it will set a proper mood and inspire the actors to actually do some acting. While Lucy and the others wanted him to get a "modern" aluminum Christmas tree (as per the fad at the time), he decides to get a real tree instead. Actually, it was basically just a tiny sapling, and not in great health. While I think getting a real tree was a good idea, the one he chose was pretty pathetic, and in real life couldn't possibly support decorations. And of course when he brings it back to... wherever the play was being "rehearsed," the others all ridicule him. So he asks if anyone can explain the true meaning of Christmas, which Linus does by reciting a passage from the Bible, about the birth of Jesus. Inspired by this, Charlie decides to take the tree home and decorate it, to prove to the others that he was right about his choice. (It doesn't seem like a tree has much to do with what he'd just learned, but... the fact that it's real is symbolic of anti-commercialism, so in that sense I guess it's kind of in the same vein as actually celebrating Christmas for its religious aspect rather than its secular aspects. Still, I can't help thinking that using the decorations that had been on Snoopy's doghouse for a display contest sort of undercuts the point.)
Anyway, in the end the other kids do realize he was right about the tree, and they manage to decorate it so that it looks really good; in fact, far better than it should be possible for it to look, but cartoons don't have to pay any heed to silly things like physics. We never do get to see the play, but at least the special has a happy ending. And I don't know what else to say, except that it's a classic, and while it may not be my favorite Christmas special ever, it's still pretty good. It has a good story and a good message, as well as some good music. Oh, and I should say that in recent years when it airs on TV, it's been edited for length, so... there's at least one scene it's been awhile since I've seen.
In 2015, there was a documentary called It's Your 50th Christmas, Charlie Brown.