This is the Christmas carol that the carol singers are singing as they walk into Luke’s.
Hark! the Herald Angels Sing was written by Charles Wesley, and first published in 1739. It was originally a slow, solemn hymn, and the opening lines were different; it was Wesley’s co-worker George Whitefield who changed it to the familiar Hark! the Herald Angels Sing in 1758. The joyful music we know today was supplied by composer Felix Mendelssohn in 1840, adapted by English musician William H. Cummings to fit the words of the carol.
The Annotated Gilmore Girls 