This is a fugue from Bach's Chorale Partitas, based on the hymn tune of the same name. Its musical distinction lies in the intricate contrapuntal development of the chorale melody.
The primary technical challenge is maintaining clarity and independence between the voices in the contrapuntal texture.
Ach, was soll ich Sünder machen (BWV 770) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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, was soll ich Sünder machen (BWV 770) lasts about 4.5 minutes.
Ach, was soll ich Sünder machen (BWV 770) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.