BWV 668 Wenn wir in höchsten Nöten sein.

Bach’s setting of this tune is “Vor’ deinen Thron’,” BWV 668, also nicknamed the “Deathbed Chorale.”

The story goes that Bach – who had gone blind, probably from complications of diabetes, and who had endured two unsuccessful operations by the English eye surgeon and charlatan John Taylor – dictated this piece to his son-in-law Johann Christoph Altnickol.

Bach’s family and friends portrayed BWV 668 as the legendary last creation of a dying composer, but in fact, Bach was revising and improving earlier material i.e. Orgelbuchlein Chorale BWV641.

They don’t look similar at first glance, because all the ornamentation is gone from the melody. But if you compare the accompaniments on the lower two staves, they’re identical. The difference is that in the later work, Bach added a lengthy introduction:

This looks totally placid on the page, but it’s a stupendous achievement: in technical terms, a fugal exposition in which the subject is answered by its own inversion.
The smoothness and grace of each individual part is awe-inspiring, and the effect when you play all the parts together is one of total serenity – an entirely different from the searching quality of the Orgelbüchlein prelude.

From a knowledgeable but unknown source.