The authenticity of this piece isn't certain. The part where the cantus firmus starts is definitely J.S. Bach, but the rest not. I think Carl Philip Emanuel Bach used his father's score and added some extra parts to it. Just as he did with BWV 639 'Ich ruf zu dir', which I uploaded before as comparison.
I was in doubt of the tempo. At first look I would play it fast like Marie-Claire Alain did, but then comes the famous part with the cantus firmus. It feels unnatural to play that part fast. So I settled for a slow tempo.