If you listen carefully on that part, "For this we know". You will hear the tenors go up a half step to Gb on "we". I went back and listened to that part a few times and it is F F Gb F.
I just listed to it several times and I don't hear it. The Sopranos going up to Eb ALMOST threw me off, but I listened a few more times and I don't think they moved.
Also, chord-wise it makes sense for it to be F all the way through (It seemed to go into F Major to walk up to Bb Minor).
What really did it is I played it on my keyboard and the chord F A C Eb fit in there beautifully. Voices I'm still learning to recognize, but chords? I'm almost sure that's a F7 there.
