The O Antiphons are Magnificat antiphons used at Vespers of the last seven days of Advent in various liturgical Christian traditions.
Each antiphon is a name of Christ, one of his attributes mentioned in Scripture. They are:
December 23 Great O Antiphon at Vespers: O Emmanuel [O King of Emmanuel]
December 22 Great O Antiphon at Vespers: O Rex Gentium [O King of Nations]
December 21 Great O Antiphon at Vespers: O Oriens [O Daystar]
December 20 Great O Antiphon at Vespers: O Clavis David [O Key of David]
December 19 Great O Antiphon at Vespers: O Radix Iesse [O Root of Jesse]
December 18 Great O Antiphon at Vespers: O Adonai [O Lord]
December 17 Great Antiphon at Vespers: O Sapientia [O Wisdom]
In the Roman Catholic tradition, the O Antiphons are sung or recited at Vespers from December 17 to December 23 inclusive (but see note below on alternative English usage).
The hymn O come, O come, Emmanuel (in Latin, Veni Emmanuel) is a lyrical paraphrase of these antiphons.
The first letters of the titles taken backwards form a Latin acrostic of "Ero Cras" which translates to "Tomorrow, I will come", mirroring the theme of the antiphons.
Origin
According to Fr. William Saunders:
“ The exact origin of the "O Antiphons" is not known. Boethius (480–524/5) made a slight reference to them, thereby suggesting their presence at that time. At the Benedictine Saint Benedict Abbey of Fleury (now Saint-Benoît-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 were 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 Western liturgical tradition since the very early Church.
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 Jesus, whose coming Christians have prepared for in Advent and whom they have addressed in these seven Messianic titles, now speaks to them: "Tomorrow, I will come." So the "O Antiphons" not only bring intensity to their Advent preparation, but bring it to a joyful conclusion.
”
A number of other antiphons were found in various medieval breviaries.
