Another setting of the chorale "Ach Gott und Herr," this piece showcases Bach's mastery of imitative counterpoint. The fugal treatment of the chorale melody is both intricate and profound.
Developing control over the balance between the independent voices is crucial.
Ach Gott und Herr (BWV 693) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Ach Gott und Herr (BWV 693) lasts about 3 minutes.
Ach Gott und Herr (BWV 693) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.