This is a masterful chorale prelude for organ, later arranged for keyboard, that brilliantly showcases Bach's contrapuntal genius. It features a complex and interwoven texture derived from the chorale melody.
Mastering the independent voice leading and maintaining clarity in the contrapuntal lines is crucial.
Aus tiefer Not schrei ich zu dir (BWV 1099) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 10.
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.
Aus tiefer Not schrei ich zu dir (BWV 1099) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.