This Christmas song is from the musical "Mame". Let me give you some context. The setting is late November, one week before Thanksgiving. Everyone thinks Auntie Mame is nuts for wanting to decorate for Christmas. But she deems it necessary, to raise everyone's spirits.
Now, we see Christmas stuff in stores in early September. Who's buying this stuff?!
Anyway, as a Christmas song, this works great - it portrays the season as a real morale booster. And it is! And Lucy - who we all love - isn't much of a singer, but she is perfect in portraying the improving mood of this delightful song.