I have a tendency to be repulsed by the nature of the lyrics in carols, as well in the way the are sung; heavy and dripping with lament. Many traditional carols seem to invent a manger scene, or some far-reaching ideal that doesn't quite ring true. Songs like "Hark! The Herald Angels Sing" and "We Three Kings" use grand language and regal imagery, perhaps a result of the time they were written, to paint a picture that betrays the humble nature in which the Christ-child supposedly came into the world.
This song's lyrics touch on some common themes of other popular Christmas carols, such as the Savior coming to earth to redeem mankind. However, this song strips down the redemption to its lowest common denominator, as well as cutting through all of the august ideas of Jesus. "His law is love and His gospel is peace" is a strong challenge to much of the teachings of American Christianity.
Exposition aside, I can't listen to this song, almost any version I have heard, without getting chills down my spine when the line "Fall on your knees/hear the angel voices/Oh night divine..." is sung.