O Radix Jesse

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.

This verse references Isaiah’s prophecies that a "shoot from the stalk
of Jesse" Isaiah 11:1 "shall stand as a signal to the peoples; the
nations shall inquire of him" Isaiah 11:10

Listen Here to a slightly less faithful (but more poetic) English
translation than the one above.