This extraordinary hymn was written by Michael Weisse in the very early 16th century in Silesia.
Silesia
I can’t find the German or English anywhere for the life of me, so sorry to leave you hanging. Nevertheless, I can’t get enough of the tune. It’s classic German and classic Baroque at the same time: solid, four-square construction, with gorgeous but sober harmony. It’s an earth-bound hymn with heaven-ward eyes, like all good prayers should be.
The Daily Tune-Up 
Found the German text: it appears on both of the scanned pages at http://www.hymnary.org/text/freuen_wir_uns_all_in_ein (and there’s some more info in the Notes tab on the page, which it says Weisse’s hymn is a German free translation of a Bohemian 15th c. text).
Thanks! A Bohemian 15th c. text is even cooler. Though Silesia is more fun to say.