This is one of Bach's most profound organ chorale preludes, setting the hymn "An Wasserflüssen Babylon." It is a masterclass in contrapuntal writing, employing complex fugal techniques and a rich harmonic language to create an intensely moving and spiritual experience.
Mastering the intricate fugal development and controlling the vast dynamic and textural range are the principal technical hurdles.
An Wasserflüssen Babylon (BWV 653) is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 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 An Wasserflüssen Babylon (BWV 653) lasts about 6 minutes.
An Wasserflüssen Babylon (BWV 653) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.