If you have my book, The Christian Delusion, in chapter one Dr. David Eller shows why language and culture matter to Christianity. In a Christian culture with Christian language people will be inclined to accept Christianity as true.
But as our culture changes so will our language, and that is a good thing even if like a chameleon Christianity will learn to adapt. In fact I'm in favor of being proactive about this. There are just too many secularists, too many Jews, too many spiritualists, too many people of different faiths in our country that the language of this holiday needs to be changed.
And one place we can insist that it be changed is how retailers market their products. Call it "The Holidays," or just "December 25th," but let's have done with the word "Christmas."