The "O Antiphons" of Advent
The Church has been singing the "O" Antiphons since at least the eighth century. They are the antiphons that are sung or said before the Magnificat canticle of Evening Prayer (part of the Liturgy of the Hours) from December 17-23, but they may also be used as short prayers each day during the week leading up to the celebration of Christmas.
You may recognize the O Antiphons because they make up the verses of the Advent hymn "O Come, O Come, Emmanuel." Each of the antiphons begins with "O," from which they get their name, and with a different title for Christ, the soon-to-be-born Son of God. They then contain a plea for Christ to "come" to teach, to rescue, to free, and to save us.
The United States Conference of Catholic Bishops describes the "O Antiphons" as magnificent theology that uses ancient Biblical imagery drawn from the messianic hopes of the Old Testament to proclaim the coming Christ as the fulfillment not only of Old Testament hopes, but present ones as well.
O Wisdom of our God Most High,
guiding creation with power and love:
come to teach us the path of knowledge!
O Leader of the House of Israel,
giver of the Law to Moses on Sinai:
come to rescue us with your mighty power!
O Root of Jesse’s stem,
sign of God’s love for all his people:
come to save us without delay!
O Key of David,
opening the gates of God’s eternal Kingdom:
come and free the prisoners of darkness!
O Radiant Dawn,
splendor of eternal light, sun of justice:
come and shine on those who dwell in darkness and in the
shadow of death.
O King of all nations and keystone of the Church:
come and save man, whom you formed from the dust!
O Emmanuel, our King and Giver of Law:
come to save us, Lord our God!