The 'O' Antiphons are the verses for the ancient hymn O Come, O Come Emmanuel. They address Christ with seven Messianic titles, based on the Old Testament prophecies which foreshadowed Him. As such, they announce Jesus in turn as our Teacher, our Redeemer, our Liberator, our Guide, our Enlightener and our Saviour, ascending through the history of redemption.
You can find them on the Church of England's website for Evening Prayer in Advent, but I have also typed them out below. If you do not say daily Evening Prayer, you might use these sentences as verses to pray on each of their respective days, or to guide you in finding a daily Bible reading in the countdown to Christmas.
December 17: O SapientiaRecalling that Jesus is our Teacher, a Jewish Rabbi, we address Him first as Divine Wisdom:
O Wisdom, coming forth from the mouth of the Most High,
reaching from one end to the other mightily,
and sweetly ordering all things:
Come and teach us the way of prudence.
cf Ecclesiasticus 24.3; Wisdom 8.1
December 18: O AdonaiNext, we go back to the time of Moses, around 1400 BC, and the extension of the redemption promised to the Jews through the Law to all people through Christ.
O Adonai, and leader of the House of Israel,
who appeared to Moses in the fire of the burning bush
and gave him the law on Sinai:
Come and redeem us with an outstretched arm.
cf Exodus 3.2, 24.12
December 19: O Radix JesseNext we come to the time of David, around 1100 BC, whose father was Jesse and into whose household, through Joseph, Jesus was born. David was liberator of his people, but Christ is liberator of all.
O Root of Jesse, standing as a sign among the peoples;
before you kings will shut their mouths,
to you the nations will make their prayer:
Come and deliver us, and delay no longer.
cf Isaiah 11.10, 45.14, 52.15; Romans 15.12
December 20: O Clavis DavidNow around 1000 BC, Hezekiah, a descendent of David, cleanses the Temple and hands on David's authority or 'key' to his steward Eliakim. This is 'key' Jesus gives to Peter, representing the Church, to set us free from sin. So it reveals Jesus as our Guide from slavery to sin to the freedom of His Kingdom.
O Key of David and sceptre of the House of Israel;
you open and no one can shut; you shut and no one can open:
Come and lead the prisoners from the prison house,
those who dwell in darkness and the shadow of death.
cf Isaiah 22.22, 42.7; Rev 3.7-8
December 21: O OriensThe 'Oriens' is the morning star, Christ as the light prophesied by Malachi to enlighten all peoples, repeated later by Simeon and, in his words known as the 'Nunc Dimittis,' by us, at Evensong, Compline and funerals.
O Morning Star,
splendour of light eternal and sun of righteousness:
Come and enlighten those who dwell in darkness
and the shadow of death.
cf Malachi 4.2
December 22: O Rex GentiumWith the light of revelation, we see Jesus as He truly is: Rex Gentium, King of the Nations, both Creator and Saviour of the world.
O King of the nations, and their desire,
the cornerstone making both one:
Come and save the human race,
which you fashioned from clay.
cf Isaiah 28.16; Ephesians 2.14
December 23: O EmmanuelFinally, the night before the Vigil of Christmas, we proclaim Jesus by His greatest title: Emmanuel, God With Us. And note that the first letter of the Messianic titles - Emmanuel, Rex, Oriens, Clavis, Radix, Adonai, Sapientia - spell out Latin words ero cras: "tomorrow, I will come."
O Emmanuel, our king and our lawgiver,
the hope of the nations and their Saviour:
Come and save us, O Lord our God.
cf Isaiah 7.14
Have a blessed Christmas.