This piece was set as a single melodic line as many Gregorian chants were constructed. Lush, modern harmonies have been added to make it the popular Christmas piece it is today. Trumpet 1 is asked to stand away from the group. This is to emulate the call and response between a soloist and congregation at a church service. It has been set for an ensemble of 4 trumpets, 2 horns, 2 trombones, euphonium, tuba and percussion.