Beginning Dec. 17 of each Advent season, and for the next seven days, a special antiphon known as an O Antiphon is read before the Magnificat during evening prayer or before the gospel at Mass. Sometimes called the Greater Antiphons, or the O’s of Advent (because they begin with that exclamation), the O Antiphons differ from the daily antiphons because they herald the coming birth of Christ. Originally written in Latin around the seventh or eighth centuries, these special antiphons are verses extracted from the Old Testament prophets — namely, Isaiah — and express the longing for the coming of the Christ. The word “come” is used in every O Antiphon. Each of the seven antiphons begins by addressing Jesus using an Old Testament title for the Messiah. These seven names or titles, all from the Book of Isaiah, are:
Dec. 17, O’ Sapientia (meaning O Wisdom), from Isaiah 11:2-3.
Dec. 18, O’ Adonai (O Lord or Ruler), 11:4-5 and 33:22.
Dec. 19, O’ Radix (O Root of Jesse), 11:1.
Dec. 20, O’ Clavis (O Key of David), 22:22.
Dec. 21, O’ Oriens (O Radiant Dawn), 9:1.
Dec. 22, O’ Rex Gentium (O King of the Nations), 2:4.
Dec. 23, O’ Emmanuel (O God with Us), 7:14.
It is widely pointed out that if you take the first letter of each Latin name and reverse the order — that is, begin with E from Emmanuel, then Rex Gentium and so on you will spell the phrase ERO CRAS, which in Latin means “I shall come tomorrow.”
Sometime before the 12th century, the exact date and author being unknown, selected verses from the seven antiphons were compiled into the hymn we today call “O Come, O Come, Emmanuel.” During the Middle Ages this hymn was an important teaching and worship aid to a society that was largely illiterate and had few Bibles. In the 19th century, the Latin version of the hymn was translated into English by an Anglican priest named John Neale. He called his original translation “Draw Neigh, Draw Neigh, Emmanuel,” but in 1854 he renamed the song, “O Come, O Come, Emmanuel,” which, given its history, is believed to be among the oldest of all the Christmas hymns.