Tomorrow begins the Octave before Christmas Eve, during which the Church recites or chants the O Antiphons preceding the Magnificat during Vespers of the Liturgy of the Hours.
The O Antiphons express the Church’s longing and expectation for the Messiah, her startled wonderment at the fullness of grace which the Christ-Child is about to bestow on the world. Their theme is the majesty of the Savior, His wisdom, His faithfulness and sanctity, His justice and mercy, His covenant with His chosen people, who in their ingratitude broke faith with Him. They are concerned with His power and love as King and Redeemer of the world, His relation to every soul as Emmanuel, God-with-us. (“With Christ Through the Year,” by Bernard Strasser)
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.
~Fr. William Saunders
For a more detailed description of the O Antiphons, and to hear them chanted in Latin, see http://fisheaters.com/customsadvent10.html