For many Christians, a prayer tradition in these final days of Advent prior to Christmas is the recitation of the great "O" Antiphons traditionally sung at evening vespers. (The hymn "O Come, O Come, Emmanuel" paraphrases the O Antiphons.)
There is a specific "O" for each day from December 17 to December 23. Monday, the antiphon began with "O Wisdom." Tuesday, the antiphon began with "O Adonai." Today (Wednesday), the antiphon began "O Root of Jesse."
Here are three YouTube videos of these ancient prayers chanted in Latin:
For December 17:
For December 18:
For December 19: