Starting today and continuing through December 23, many Western churches use special seasonal antiphons for the Magnificat at celebrations of Vespers/Evening Prayer/Evensong. Known as the Great O Antiphons, they are drawn from passages in the Hebrew Scriptures traditionally interpreted by the Church as referring to the coming of the Messiah. They occur in liturgical texts as early as the ninth century and became solidly entrenched in monastic and parish worship during the middle ages.

A good reference to the Antiphons may be found here on the excellent Chantblog site, which includes links to recordings. (To avoid confusion, in England and some other places the Great O's begin on December 16, with the extra O Virgo Virginum used on December 23. I follow the practice of the American Episcopal Church).

The English text below comes from the sadly out-of-print The Prayer Book Office (Seabury Press 1988), an augmented version of the 1979 Book of Common Prayer which I have long used for my personal recitation of the Office. The antiphons are found on pp 131-132.

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December 17. O Sapientia

O Wisdom, you came forth from the mouth of the Most High, and reach from one end of the earth to another, mightily and sweetly ordering all things: Come and teach us the way of prudence.

December 18. O Adonai

O Adonai, and Leader of the house of Israel, you appeared in the bush to Moses in a flame of fire, and gave him the law on Sinai: Come and redeem us with an outstretched arm.

December 19. O Radix Jesse

O Root of Jesse, you stand as an ensign to the peoples; before you kings will shut their mouths, and nations bow in worship: Come and deliver us, and tarry not.

December 20. O Clavis David

O Key of David, and Scepter of the house of Israel, you open and no one can shut, you shut and no one can open: Come and bring the captives out of the prison house, those who sit in darkness and the shadow of death.

December 21. O Oriens

O Dayspring, Brightness of the Light Eternal, and Sun of Righteousness: Come and enlighten those who sit in darkness and the shadow of death.

December 22. O Rex Gentium

O King of the nations, and their Desire, you are the cornerstone who makes us both one: Come and save the creature whom you fashioned from clay.

December 23. O Emmanuel

O Emmanuel, our King and Lawgiver, the Desire of all nations and their Salvation: Come and save us, O Lord our God.