This is lovely.
A motet on Isaiah 41:10 and 43:1, set for double choir.
Do not fear, for I am with you;
do not be dismayed, for I am your God.
I will strengthen you and help you;
I will uphold you with my righteous right hand.
Do not fear, for I have redeemed you;
I have summoned you by name; you are mine.
Double choir means you divide your choir in two halves so as to make the music even more complicated (as if Bach's music wasn't already complicated enough!)
Here they have one voice per part. It gives wonderful clarity, but you can lose attack and ... guts...
I'm pretty sure the band just doubles the voice parts. Bach didn't write band parts.