This motet-style piece by Mozart showcases his early mastery of vocal-instrumental balance and clarity. Its distinction lies in the purity of the melodic line and the transparency of the accompaniment.
Maintain a 'vocal' quality in the right hand melody while keeping the accompaniment light and crisp.
Benedictus sit Deus is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 6.
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 Benedictus sit Deus lasts about 4 minutes.
Benedictus sit Deus is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.