O Radix Jesse, qui stas in signum populorum,
super quem continebunt reges os suum,
quem Gentes deprecabuntur:
veni ad liberandum nos, jam noli tardare.

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.

There shall come forth a shoot from the stump of Jesse, and a branch shall grow out of his roots. Isaiah 11:1

In that day the root of Jesse shall stand as an ensign to the peoples; him shall the nations seek, and his dwellings shall be glorious. Isaiah 11:10

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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.