Merry Christmas to you and your family, and best wishes for a wonderful New Year for all of us.
It is a Christian song largely because it was written by a repentant slaver who found Christ. There is no reason why a person of any other faith should find it unusual to love this song about personal redemption in a good cause. Think of the song as a mitzvah.
Il Divo does a great job of enunciating the words and thus illustrating the meaning of the song. How can one not be filled with tears and joy?