The Great “O” Antiphons were sung before and after the Psalm at Vespers during the last seven days of Advent. They were used to create the hymn “O Come, O Come, Emmanuel,” which is the Hymn of the Day for the Fourth Sunday in Advent: Rorate Coeli. The “O” Antiphon for December 19 is:
O Root of Jesse, standing as an ensign before the peoples, before whom all kings are mute, to whom the nations will do homage:
Come quickly to deliver us.