A profound and emotionally charged chorale prelude, BWV 38 is a cornerstone of Bach's organ works, deeply exploring the spiritual lament of the chorale. Its powerful expression comes from the rich harmonic language and contrapuntal density.
Achieving a singing tone and conveying the pathos of the chorale melody requires sensitive phrasing.
Aus tiefer Not schrei ich zu dir (BWV 38) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 9.
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 38) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.