Here is, almost certainly, Bach's last composition for voices.

"Et incarnatus est" is the short choral movement in the Mass in B minor which precedes and sets up the central "Crucifixus." Being not quite yet Christ's death, the "Et incarnatus est" depicts the sighing descent of Christ being made man. A mournful coincidence: this music also imminently preceded Bach's death. He likely finished it in 1750, the year of his death, to complete the compilation of the masterfully crafted and structured Mass in B Minor. 

Christian focuses on one of the single most haunting and uncommon chords: the augmented sixth chord, which in Baroque music is found only in the most sorrowful moments.

**Music theory note!** When we discuss the other augmented sixth chord example from "O Schmerz" in the St. Matthew Passion, this chord has that augmented sixth interval inverted, so while the effect is similar, this interval becomes a diminished 10th (from B in the bass to D flat in the tenor)! 

"Et incarnatus est" choral movement from the Credo section of Bach's Mass in B minor BWV 232, as performed by the Netherlands Bach Society