As several posters have said, Christmas wasn't about Christianity originally; the Christian church, in its usual habit of appropriating the beliefs and rituals of "pagan" tribes and then converting them by telling them "Look, you've believed in our god all along", created Christmas out of a combination of Nordic, central European and Roman festivals. The most famous is probably Saturnalia, of course, but there are also connections to Mithras, Scandinavian blot, and of course Coca-Cola's early advertising campaigns.
So yeah... Christmas as a celebration of the birth of Jesus is - cynically speaking - largely a Christian marketing campaign. In that sense, the purpose of Christmas as we know it has changed little since the first millennium - the difference is that then they were selling a religion, now they're selling cuddly toys, sub-par smartphones and bedroom novelty items of questionable humour.
Personally? I'm undecided on religion. As far as I'm concerned, there's nothing to stop a god or gods from existing, but if they're really omnipotent they don't need worship. And if they deserve worship, they won't demand it - so I tend to largely ignore religion.
I love Christmas, though, largely because of the traditions. The Christmas tree (or, this year for irritating reasons of space and budget, the Christmas bush - the thing's less than three foot tall), the food, the decorations, Donald Duck on TV at 3PM on Christmas Eve... Unfortunately the classic Christmas happiness has been pretty forced of late, what with economic hassles and health scares and all sorts of stuff, but yeah.
And it's always fun to be given stuff, of course, but I guess there's little chance of that either this year.
Anyway. Sod religion, go Christmas. ;-)