O Come All Ye Faithful is one of the most-used Christmas Carols of all time. Here are a few ideas for arranging it on the piano. Please watch this 10-minute video:

Arranging Christmas Carols Course

Passing tones are notes that are not in the chord, but “pass through” between chord notes. An ostinato is a sustained bass note — usually the 5th of the chord — that is held while different chords occur over the top of it. Watch this short video on O Come All Ye Faithful and you’ll understand quickly.

Musical passing tones and ostinato in “O Come All Ye Faithful”