The differences in the lyric are subtle, but speak volumes about the bittersweet feelings that the holidays seem to bring. Unlike what most people think, the song isn't joyous, it's more along the lines of, "Just get through it."
Just hold on till the time when we all, hopefully, get to be with our loved ones once again. The ones we remember so vividly from Christmases past. Just have a little Christmas. That's all. That's something that we can do no matter what. A little Christmas.