Here's the score, from the Benedictines of Brazil:
The text - at least part of it - is from Psalm 110. The first section does seem to be a composition, although one based on Psalm 110, verse 3-ish. I'll need to look more closely at this to see if I can find out where it came from - or whether I'm looking at a variant translation of this Psalm (don't think it's that, though). JoguesChant offers this translation of the text:
Sovereign strength is yours on the day of your great might. Amidst the splendours of the heavenly sanctuary, from the womb, before the morning star, I have begotten you. The Lord said unto my Lord: "Sit at my right hand, until I make your enemies a stool for your feet".
Here's Handel's version of this:
This is my favorite, though - the Tecum Principium from Saint-Saens' Christmas Oratorio:
Wow, I just love this little piece! Saint-Saens wrote it when he was only 23 or so. It's little, but it's very, very nice. Here's another movement - the 9th section, "Consurge, filia Sion" - and the nicest little collection of Alleluias you'll ever hear:
And then, you wouldn't want to miss Part 10, either: Tollite Hostias:
The texts and translations:
Consurge, Filia Sion.
Lauda in nocte,
in principio Vigiliarum.
Egrediatur ut splendor justus Sion,
et Salvator ejus ut lampas accendatur.
Tollite hostias, et adorate Dominum in atrio sancto ejus.
Lætentur cœli, et exultet terra, a facie Domini, quoniam venit,
Arise, O daughter of Sion.
Give praise in the night,
in the beginning of the watches.
Let the righteous man go forth from Sion as brightness,
and let her Saviour go up as a light.
Lift up the offerings, and worship the Lord in this holy courtyard.
Let the heavens be glad, and let the earth rejoice, at the face of the Lord, for he cometh.
Blessed Christmas! Here's Guido Reni's "Adoration of the Shepherds":