This aria, BWV 508, is often mistakenly attributed to Bach but is actually by Gottfried Heinrich Stölzel. It is cherished for its deeply emotional and introspective quality, often used as a vocal or instrumental solo.
Emphasize a singing legato and delicate phrasing to capture the piece's gentle sadness.
Bist Du bei mir is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 3.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 Bist Du bei mir lasts about 2 minutes.
Bist Du bei mir is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.