Bach's Johannespassion (Part 2: the mystery of Bach)

I had the pleasure of hearing Bach's Johannespassion on Palm Sunday in the Grossmünster of Zurich. It was sung by the Bach Collegium, in which my friend Laura sings. On Easter Sunday this year I will be in Amsterdam, and the Concertgebouw is giving the Matthäuspassion, so I will hear these two works a week apart, each for the first time. Obviously, two sung passion plays by Bach are going to have as many similarities as differences (Bach told the story of Christ's crucifixion at least three times in large-scale works), and before I sink into this later, more intimate and pensive work (Matthäuspassion), I'd like to spend more time thinking about the more intensely dramatic Johannespassion that affected me so.

For reference I really admire this recording from Munich, conducted by Karl Richter, sung by an enormous chorus of ice-cold Germans:

I find it impossible to imagine what sort of a man Bach was, harder still to imagine the emotional world he inhabited (and the far less religious one that usurped it). The music itself would point to a man of the deepest, most mystical religious devotion. The non-Biblical libretti circle over and over again around the humility needed to honor God, around the gracious gift of undeserved mercy. The thought that, until Mendelssohn, this massif of artistic ambition went mostly unperformed beyond Leipzig for a hundred years, der Schall nearly verschollen -- it boggles the mind that the question of posterity did not appear to concern him, or that any steps he took for his own posterity were only meagerly successful, and left no traces in his music. Is this Bach an artist without ego? Would our modern idea of an artist concede even the possibility of such a thing? Writing music for any given Sunday, music that lasts for a thousand years? Is this Bach merely a talented family man working to please a court patron, his talent a coincident miracle?