Music and spiritual expression go hand-in-hand. The Greeks gave us the Muses, and one was Polyhymnia who inspired religious songs. The Native Americans developed intricate rhythm and vocal expressions for their ceremonies. Buddhists use singing bowls or bells to begin and end meditations.
As someone who has experience in theater, I find that music underscores mood, and so it seems natural that in developing a religious ceremony, music would be a central feature in transporting a congregation or an individual into a sublime experience. It is helpful to feel uplifted and removed from everyday concerns, and the artistry involved in theater, orchestration, or the construction of any ceremony provides us with a dramatic arc–an emotional path to follow.
For Christian Americans, with all the emotional resonances attached to the celebration of Christmas (personal and religious), music would be transporting, and probably span the spectrum of moods, from morose to exuberant, based on memories stirred by song.
If we really want to understand why music and ceremony are so tightly interlinked, then we have to understand how our brains process sound, and in this I am out of my realm.