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 "O Herre Gott, dein göttlich [Wort]." Here's the arrangement from TLH:
And here's the arrangement from Telemann's Fast allgemeines Evangelisch-Musicalisches Lieder-Buch:
There's quite a bit in the seventh verse (particularly near the end) and the tenth verse that I'm not too confident about.
The beginning of the sixth verse ("He is chosen by God / For the high priesthood") seems to refer to Hebrews 5. The title "Saron's schönste Blum" at the end of the verse is literally "Sharon's most beautiful flower," but since it's a reference to Song of Solomon 2:1 where the title is "a rose of Sharon," that's how I translated it: "Sharon's most beautiful rose."
Part of the eighth verse seems to be patterned on Philippians 2:10-11: "10 so that at the name of Jesus every knee should bow, in heaven and on earth and under the earth, 11 and every tongue confess that Jesus Christ is Lord, to the glory of God the Father." The last line, though, seems to come from Psalm 113:3: "From the rising of the sun to its setting, the name of the LORD is to be praised!"
The first couple lines of the ninth verse ("His throne must last eternally; / His scepter stands firmly") bear some resemblance to Hebrews 1:8 (quoting Psalm 45:6): "But of the Son he says, 'Your throne, O God, is forever and ever, the scepter of uprightness is the scepter of your kingdom.'"
I think the line "He tests heart and kidneys," in the twelfth verse refers to a Hebrew idiom. The last line of the verse ("Those who deny themselves") seems to come from Matthew 16:24 ("Then Jesus told his disciples, 'If anyone would come after me, let him deny himself and take up his cross and follow me.'") or Luke 9:23 ("And he said to all, 'If anyone would come after me, let him deny himself and take up his cross daily and follow me.'").
As far as I can tell, this hymn isn't present in The Lutheran Hymnal, Lutheran Worship, or The Lutheran Service Book. According to the Gesangbuch, the text is sung to the tune "Herr Christ, der einig G[ottes Sohn]." Here's the arrangement from Telemann's Fast allgemeines Evangelisch-Musicalisches Lieder-Buch:
This is the first hymn in a new section: "Lieder am Fest der Verkündigung Mariä. (Am 25. März.)" Songs for the Feast of the Annunciation of Mary (on 25 March)
German text in the Gesangbuch:
Freu dich, du werthe Christenheit,
dies ist der Tag des Herren,
der Anfang unsrer Seligkeit,
den Gott zu seinen Ehren
nach seinem Rath
erwählet hat: o Gott, laß wohl gelingen!
Hilf uns mit Fleiß
zu deinem Preis
ein 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 Schoß
den 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 dich
demüthliglich:
lehr uns deim Wort vertrauen,
bis wir zugleich
im Himmelreich
das 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 glory
According to His counsel
Has chosen:
O God, let it well succeed!
Help us with diligence
To Your praise
Sing a cheerful song.
God is righteous in his Word;
What once He promised
That 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 womb
Receives the great guest.
She hears from the angel Gabriel
She 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 story
Yet believes the words,
As she hears,
God will do it well.
For us, well being of the merciful time
That we attain the decoration
That You, O God of eternity,
Are become our Brother.
We ask You
Humbly:
Teach us to believe Your Word
Until together we
In Heaven
Look 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:
I couldn't find a translation for "lahn" in the second verse. I translated it as "let" based only on the context. Same for "fürgestellt" in the third verse, which I translated as "put forth."
I had to shuffle some of the lines around in the third verse and the end of the fourth verse (the last two lines) to get a smoother English translation.
This hymn appears as "In Peace and Joy I Now Depart" in The Lutheran Hymnal (#137), Lutheran Worship (#185), and The Lutheran Service Book (#938). In each hymnal and as the Gesangbuch notes, the text is sung to "its own melody." Here's the arrangement from TLH: