December 18
"O Adonai, and Leader of the house of Israel, Who didst appear to Moses in the flame of the burning bush, and didst give unto him the Law on Sinai: come and with an outstretched arm redeem us."
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 importance of "O Antiphons" is twofold: Each one highlights a title for the Messiah: O Sapientia (O Wisdom), O Adonai (O Lord), O Radix Jesse (O Root of Jesse), O Clavis David (O Key of David), O Oriens (O Rising Sun), O Rex Gentium (O King of the Nations), and O Emmanuel. Also, each one refers to the prophecy from Isaiah of the coming of the Messiah.
