This organ prelude and fugue by J.S. Bach is a virtuosic contrapuntal masterpiece, showcasing brilliant technical demands and profound musical invention. The fugue subject is highly energetic and memorable.
Mastering the rapid figuration and maintaining clarity in the dense contrapuntal passages is the primary challenge.
Allein Gott in der Höh sei Ehr' (BWV 771) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 Gott in der Höh sei Ehr' (BWV 771) lasts about 4 minutes.
Allein Gott in der Höh sei Ehr' (BWV 771) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.