One week before Christmas, in special preparation for the feast, many Catholics begin praying the O Antiphons. They are so called because each one begins with an “O” invoking the coming of Christ by appropriate titles derived from the Old Testament prophecies.  

O Wisdom,  O Lord of Might,  
O Flower of Jesse’s Stem, O Key of David,  
O Dayspring, O Desire of the Nations,  
O Emmanuel!