The Roman Church has been singing the "O" Antiphons since at least the eighth century. They are the antiphons that accompany the Magnificat canticle of Evening Prayer from December 17-23. They are a 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. Their repeated use of the imperative "Come!" embodies the longing of all for the Divine Messiah.
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!
—From Catholic Household Blessings & Prayers