"a setting of the Gradual for the fest of the Epiphany"

The Christian feast of the Epiphany celebrates the coming of the Wise Men to worship at the manger containing the baby Jesus. 

Adoration of the Magi by Albrecht Durer
Public DomainAdoration of the Magi by Albrecht Durer

 Litergical chants, such as the Gregorian chant Omnes de Saba, the Gradual for the feast of the Epiphany, reenact the drama of the story.