You could read up on the teachings of the human Jesus Christ that have to do with being peaceful and kind to your neighbor, decide that you like these teachings

You could read up on the teachings of the human Jesus Christ that have to do with being peaceful and kind to your neighbor, decide that you like these teachings, and wish people merry Christmas with these teachings in mind. (I'm afraid I mostly substitute "cultural osmosis" for "reading up".) Merry Christmas, by the way.