O Antiphons?

There is a special feature in the Evening Prayer (Vespers) of the Church over the seven days before Christmas. For each of the seven days there is a special antiphon prayed which together are called the O Antiphons. Each of the O Antiphons start with a title of Christ: O Wisdom; O Sacred Lord; O Root of Jesse; O Key of David; O Radiant Dawn; O King of Nations; O Emmanuel. Each title contains a rich treasure of meaning shedding light on the Person of Christ worthy of meditation and study. These titles form the skeleton of the traditional Advent hymn O Come, O Come, Emmanuel. Fr Nicolas Maurice