This beautiful duet is from the cantata BWV149 "Man singet mit Freuden vom Sieg in den Hütten der Gerechten". Bach composed it in 1728/29 for Michaelmas Day.
This duet is beautiful. Beautiful because the alto and tenor voices are close together and beautiful also because of the instrumentation.
Once again I chose the Friesach organ because it is the most versatile with its 3 manuals and 44 sounding voices. We hear the singing voices on the 3rd manual with the Trompette en chamade. The bassoon sounds on the swell and the bass is in the pedal, which is coupled with the Hauptwerk.