This entry refers to a piece by Johann Sebastian Bach titled "Ach Gott und Herr." Given the numbering of other BWV pieces, it's likely another setting or arrangement of the chorale, emphasizing Bach's consistent engagement with this hymn.
Focus on the clear exposition of the fugal subject and the development of its contrapuntal texture.
Ach Gott und Herr 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 lasts about 3 minutes.
Ach Gott und Herr is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.