O Rex Gentium, et desideratus earum,
lapisque angularis, qui facis utraque unum:
veni, et salva hominem,
quem de limo formasti.

O King of the nations, and their desire,
the cornerstone making both one:
Come and save the human race,
which you fashioned from clay.

For to us a child is born, to us a son is given; and the government will be upon his shoulder, and his name will be called "Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace." Isaiah 9:6

He shall judge between the nations, and shall decide for many peoples; and they shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war any more. Isaiah 2:4

---

During the evening prayer of the Liturgy of Hours, which is also known as Vespers, the Church prays the beautiful prayer of Mary known as the Magnificat. Preceding the Magnificat, there is an antiphon which is simply a short verse which connects the prayer to the particular feast day or liturgical season. On the last seven days of Advent, from December 17th through December 23rd, the antiphon for Vespers is one of the so-called "O Antiphons". It is related to a particular title of Christ's, and the antiphon ends with a plea for the Messiah to come. Click here to read more about the O Antiphons.