Bach's chorale prelude BWV 1100 is a delicate and introspective setting of the hymn tune. Its intricate melodic lines and subtle harmonic colors create a profound sense of peace.
Achieving clarity in the contrapuntal texture and executing the subtle ornamentation with grace are the main challenges.
Allein zu dir, Herr Jesu Christ (BWV 1100) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
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 Allein zu dir, Herr Jesu Christ (BWV 1100) lasts about 1 minute.
Allein zu dir, Herr Jesu Christ (BWV 1100) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.