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. 48O-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. Also, each one refers to the prophecy of Isaiah of the coming of the Messiah.
O Sapientia: O Wisdom, O holy Word of God, you govern all creation with your strong yet tender care. Come and show your people the way to salvation. Isaiah had prophesied, The spirit of the Lord shall rest upon him: a spirit of wisdom and of understanding, a spirit of counsel and of strength, a spirit of knowledge and fear of the Lord, and his delight shall be the fear of the Lord. (11:2-3), and Wonderful is His counsel and great is His wisdom. (28:29).
O Adonai: O sacred Lord of ancient Israel, who showed yourself to Moses in the burning bush, who gave him the holy law on Sinai mountain: come, stretch out your mighty hand to set us free. Isaiah had prophesied, But He shall judge the poor with justice, and decide aright for the lands afflicted. He shall strike the ruthless with the rod of his mouth, and with the breath of his lips he shall slay the wicked. Justice shall be the band around his waist, and faithfulness a belt upon his hips. (11:4-5); and Indeed the Lord will be there with us, majestic; yes the Lord our judge, the Lord our lawgiver, the Lord our king, he it is who will save us. (33:22).
O Radix Jesse: O Flower of Jesses stem, you have been raised up as a sign for all peoples; kings stand silent in your presence; the nations bow down in worship before you. Come, let nothing keep you from coming to our aid. Isaiah had prophesied, But a shoot shall sprout from the stump of Jesse, and from his roots a bud shall blossom. (11:1), and A On that day, the root of Jesse, set up as a signal for the nations, the Gentiles shall seek out, for his dwelling shall be glorious. (11:1O). Remember also that Jesse was the father of King David, and Micah had prophesied that the Messiah would be of the house and lineage of David and be born in David's city, Bethlehem (Micah 5:1).
O Clavis David: O Key of David, O royal Power of Israel controlling at your will the gate of Heaven: Come, break down the prison walls of death for those who dwell in darkness and the shadow of death; and lead your captive people into freedom. Isaiah had prophesied, AI will place the Key of the House of David on His shoulder; when he opens, no one will shut, when he shuts, no one will open. (22:22), and His dominion is vast and forever peaceful, from David's throne, and over His kingdom, which he confirms and sustains by judgment and justice, both now and forever. (9:6).
O Oriens: O Radiant Dawn, splendor of eternal light, sun of justice: come, shine on those who dwell in darkness and the shadow of death. Isaiah had prophesied, The people who walked in darkness have seen a great light; upon those who dwelt in the land of gloom a light has shown. (9:1).
O Rex Gentium: O King of all the nations, the only joy of every human heart; O Keystone of the mighty arch of man, come and save the creature you fashioned from the dust. Isaiah had prophesied, for a child is born to us, a son is given us; upon his shoulder dominion rests. They name him Wonder-Counselor, God-Hero, Father-Forever, Prince of Peace. (9:5), and He shall judge between the nations, and impose terms on many peoples. They shall beat their swords into plowshares and their spears into pruning hooks; one nation shall not raise the sword against another, nor shall they train for war again. (2:4).
O Emmanuel: O Emmanuel, king and lawgiver, desire of the nations, Savior of all people, come and set us free, Lord our God. Isaiah had prophesied, The Lord himself will give you this sign: The Virgin shall be with child, and bear a son, and shall name him Emmanuel.
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.