It's so hard to pick! I do love Thankful Heart from a Muppet Christmas Carol particularly. To me, it really embodies the spirit of Christmas. Plus, it has Muppets! All the songs from that film are great though.
Also Someday at Christmas by Stevie Wonder, even though it makes me cry.
“Action on behalf of life transforms. Because the relationship between self and the world is reciprocal, it is not a question of first getting enlightened or saved and then acting. As we work to heal the earth, the earth heals us.” ~ Robin Wall Kimmerer