German text in the Gesangbuch:
Freu dich, du werthe Christenheit,dies ist der Tag des Herren,der Anfang unsrer Seligkeit,den Gott zu seinen Ehrennach seinem Ratherwählet hat:
o Gott, laß wohl gelingen!Hilf uns mit Fleißzu deinem Preisein fröhlichs Lied zu singen.Gott ist gerecht in seinem Wort,was er einmal zusaget,das ist gewiß an allem Ort,obschon die Welt verzaget;heut Gottes Sohn,der Gnadenthron,zu uns auf Erd gelanget.O Wunder groß!Marien Schoßden großen Gast empfanget.
Sie hört vom Engel Gabriel,sie sollt Jesum gebären,der ganzen Welt Immanuel,den mächtig großen Herren.Das Jungfräulein,so keusch und rein,erschrak ob der Geschichten,doch glaubt dem Wort,wie sie gehört,Gott wird es wohl verrichten.
Wohl uns der gnadenreichen Zeit,daß wir erlangt den Orden,daß du, o Gott von Ewigkeit,bist unser Bruder worden.Wir bitten dichdemüthliglich:lehr uns deim Wort vertrauen,bis wir zugleichim Himmelreichdas Wunderwerk anschauen.Petrus Hagius, +1620.
My prose translation:
Rejoice, you dear Christendom;This is the day of the Lord,The beginning of our salvation,Which God to His gloryAccording to His counselHas chosen:O God, let it well succeed!Help us with diligenceTo Your praiseSing a cheerful song.God is righteous in his Word;What once He promisedThat is certain in every place,Although the world despairs;To-day God's Son,The throne of mercy,Reaches us on earth.O wonder great!Mary's wombReceives the great guest.She hears from the angel GabrielShe should give birth to Jesus,Immanuel for the whole world,The mighty, great Lord;The virgin,So chaste and pure,Startled on account of the storyYet believes the words,As she hears,God will do it well.For us, well being of the merciful timeThat we attain the decorationThat You, O God of eternity,Are become our Brother.We ask YouHumbly:Teach us to believe Your WordUntil together weIn HeavenLook at the miracle.Petrus Hagius, +1620.
There's not too much of a resemblance between the original texts, but "Rejoice, you dear Christendom; / This is the day of the Lord" ended up a bit similar to Psalm 118:24: "This is the day that the LORD has made; let us rejoice and be glad in it."
"Startled" may be too weak of a translation for "erschrak" in the third verse, but I felt that "scared" had too much of a negative connotation.
I'm not too confident in my translation of the first few lines of the fourth verse. I couldn't really tell what part of speech "Wohl" is. I translated it as a noun because that seemed to make the most sense in this context, but it can also be an adjective or an adverb (normally, as an adjective or adverb, the word wouldn't be capitalized, but here it starts the line). Much of the time, I'm not sure how to translate "wohl" anyway. Of my dictionaries suggestions for "Orden," "decoration" was the best, but I'm not sure that this really fits the context.
As far as I can tell, this hymn isn't in The Lutheran Hymnal, Lutheran Worship, or The Lutheran Service Book. According to the Gesangbuch, the text is sung to the tune "Durch Adams Fall ist ganz." Here's the arrangement from Telemann's Fast allgemeines Evangelisch-Musicalisches Lieder-Buch: