This chorale prelude by J.S. Bach, part of his Little Organ Book, transforms a familiar hymn tune. Its musical distinctiveness lies in the way Bach elaborates the melody with rich harmonies and contrapuntal texture.
Focus on maintaining a clear melodic line amidst the contrapuntal texture and precise articulation.
Ach, daß nicht die letzte Stunde (BWV 439) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 6.
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, daß nicht die letzte Stunde (BWV 439) lasts about 3 minutes.
Ach, daß nicht die letzte Stunde (BWV 439) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.