This song is based on the angels appearing to the shepherds to announce the birth of the messiah and praise him. Gloria in excelsis deo!

The angel said to the shepherds, “Do not be afraid; for behold, I proclaim to you good news of great joy that will be for all the people.  For today in the city of David a savior has been born for you who is Christ and Lord.  And this will be a sign for you: you will find an infant wrapped in swaddling clothes and lying in a manger.”  And suddenly there was a multitude of the heavenly host with the angel, praising God and saying: “Glory to God in the highest and on earth peace to those on whom his favor rests.”  Luke 2:10–14