The O Antiphons (2)

In some liturgical traditions the O Antiphons are used in the evening office (the hours, the daily office) during the last week leading up to Christmas Eve.

Each antiphon is a name of Christ, one of his attributes mentioned in Scripture.

• December 17: O Sapientia (O wisdom)
• December 18: O Adonai (O Adonai)
• December 19: O Radix Jesse (O Root of Jesse)
• December 20: O Clavis David (O Key of David)
• December 21: O Oriens (O Morning Star)
• December 22: O Rex Gentium (O King of the nations)
• December 23: O Emmanuel (O Emmanuel)

The exact origin of the "O Antiphons" is not known. Boethius (480–524/5) made a slight reference to them, by suggesting their use. At the Benidictine abbey in  Fleury (now St Benoit-sur-Lorie), these antiphons were recited by the abbot and then a gift was given to each member of the community. By the eighth century, they were in use in the Advent liturgy. The usage of the "O Antiphons" was so prevalent in monasteries that the phrases "Keep your O" and "The Great O Antiphons" were common parlance. One may thereby conclude that in some fashion the "O Antiphons" have been part of Western liturgical tradition since the very early Church ( Father Willam Saunders, "What are the O Antiphons?")

 These antiphons were arranged with a definite  purpose in mind. If  you start with the last title and take the first letter of each one—Emmanuel, Rex, Oriens, Clavis, Radix, Adonai, Sapientia—the Latin words ero cras are formed.They mean, "Tomorrow, I will come". Jesus, whose coming is at the  heart of Advent and who has been  addressed in these seven Messianic titles,speaks to the celibrant: "Tomorrow, I will come."  The " O Antiphons" not only engage the heart in Advent preparation, but bring a joyful conclusion as well.

complied from serveral sources 

the last week O antiphons (1) article