This is the Christmas carol that the bell ringers are practicing when Lorelai walks past them on her way to Luke’s.
The First Noel or The First Nowell is a traditional English Christmas carol, dating to perhaps the 15th century, but possibly earlier. It tells the story of the shepherds and the three wise men being led to the baby Jesus by a wondrous star, taken from different parts of the Gospels. The carol is of Cornish origin, and was first published in 1823, although today the 1871 arrangement is more common.
The Annotated Gilmore Girls 