O Come!! The O Antiphons
Quick Explanation of the O Antiphons, said at Evening Prayer or Vespers from December 17-23 at the last part of Advent. Acrostic ERO CRAS--Tomorrow, I will come. The O Antiphons are seven precious jewels of our Catholic Liturgy, counting down the last seven days before Christmas with building anticipation. Because each antiphon begins with an “O” this group of antiphons are called O Antiphons.
O Rex Gentium King Florence Berger O Clavis David Bernard Strasser Jennifer Gregory Miller Mother Church
Source: catholicculture.org