From Luther's Deutsche Messe

At the time of the Reformation of the 16th century, Martin Luther translated the hymns of the mass into the German language and generally put them in metrical form. For the Latin Sanctus, he expanded the text to encompass more of the passage in Isaiah 6 from which it is taken. This was the result: "Isaiah, Mighty Seer, in Days of Old." Nancy and I heard this sung by a wonderful church choir this morning, as part of the celebration of Trinity Sunday. Generations of Lutherans are familiar with this hymn; it deserves to be known more widely in the rest of the body of Christ.