For worship at Florence we have been using the ancient tradition of the O Antiphons. The hymn "O come, O come, Emmanuel" sings out these longings, and is often used week by week in congregations as one, then two, then three, then four Advent candles are lit. However, the tradition has a deeper structure, which you will find reflected below.
For each day from December 17 through December 23 you will find here a reflection on each of these prayers.
What are the "O Antiphons"?
The “O Antiphons” refer to the seven antiphons that are recited (or chanted) preceding the Magnificat during Vespers of the Liturgy of the Hours. They cover the special period of Advent preparation known as the Octave before Christmas, Dec. 17-23, with Dec. 24 being Christmas Eve and Vespers for that evening being for the Christmas Vigil.
The exact origin of the “O Antiphons” is not known. Boethius (c. 480-524) made a slight reference to them, thereby suggesting their presence at that time. At the Benedictine abbey of Fleury (now Saint-Benoit-sur-Loire), these antiphons were recited by the abbot and other abbey leaders in descending rank, and then a gift was given to each member of the community. By the eighth century, they are in use in the liturgical celebrations in Rome. 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 our liturgical tradition since the very early Church.
The importance of “O Antiphons” is twofold: Each one highlights a title for the Messiah: O Sapientia (O Wisdom), O Adonai (O Lord), O Radix Jesse (O Root of Jesse), O Clavis David (O Key of David), O Oriens (O Rising Sun), O Rex Gentium (O King of the Nations), and O Emmanuel. Also, each one refers to the prophecy of Isaiah of the coming of the Messiah. …
According to Professor Robert Greenberg of the San Francisco Conservatory of Music, the Benedictine monks arranged these antiphons with a definite purpose. If one starts with the last title and takes the first letter of each one - Emmanuel, Rex, Oriens, Clavis, Radix, Adonai, Sapientia - the Latin words ero cras are formed, meaning, “Tomorrow, I will come.” Therefore, the Lord Jesus, whose coming we have prepared for in Advent and whom we have addressed in these seven Messianic titles, now speaks to us, “Tomorrow, I will come.” So the “O Antiphons” not only bring intensity to our Advent preparation, but bring it to a joyful conclusion.
This information was provided by the following website: http://www.catholiceducation.org/articles/religion/re0374.html