The O Antiphons are best known as the inspiration for the Advent hymn “O Come O Come Emmanuel.” Composed in the sixth or seventh century, they are used in vespers (evening prayer) and the Masses for December 17-23. Each begins with a title for Christ, drawn from the Book of Isaiah, and the first letters of the titles in Latin are SARCORE. Read backward, that is ero cras, which means “Tomorrow I come” (or “shall be”). (Traditionally, feasts were said to begin on the eve of their celebration, so Christmas begins at sundown on Christmas Eve.)
The O Antiphon for December 17, “O Wisdom,” is drawn from Isaiah 11:2-3 and 28:29.
O Wisdom, Who didst come out of the mouth of the Most High, reaching from end to end and ordering all things mightily and sweetly: come and teach us the way of prudence.