After an eight-month battle with an invasive and hard-to-reach tumor, my sister Ada Smit (born 1939), passed away in a provincial hospice in Groningen in early March.
This one's for her.
DEMO Sample set:
Hauptwerk Coupler (P-RW): Subbas 16', Roerfluyt 8';
Manual: Gedackt 8'(HW);
C.F.: Vox Humana 8' (BW).
When I began to explore this stunningly beautiful composition I believed, together with many millions of Bach ‘fans’ throughout the ages  - organists, historians and music ‘experts’ alike - that this was Bach's famous ‘deathbed chorale’, dictated by a now blind Bach to his pupil and son-in-law Johann Christoph Altnikol, just before he died.
Alas, this view of BWV 668’s origins appears to be a fable, carefully crafted by Bach's descendants in an attempt to consolidate and perpetuate his legendary status as musician and composer . And because the choral was posthumously added to the Eighteen Leipziger Chorale, as the very last composition in this series (five compositions were added posthumously), I also suspect that Bach's music publisher was in on the construction of this secret: its place as the 18th and final chorale in the series reinforces the notion of the "deathbed composition".
The melody of this chorale fits more than one hymn, including Bach's earlier composition ‘Wenn wir in höchsten Nöthen sein’ (BWV 641). As our Contrebombarde colleague Edo Luynenberg writes with his upload , this composition is closely related to BWV 668. In the Genevan Psalter the tune is used for Psalm 140.
 Edo Luynenberg: https://www.contrebombarde.com/concerthall/music/38037