Listening last night to Glenn Gould's reading of The Well-tempered Clavier, Books I and II, I wondered, and not for the first time, what it was about Gould's Bach that made it so compelling, even — dare I say it? — transcendent. There are a number of readings of Bach's keyboard works by harpsichordists and pianists that are by any fair-minded and honest assessment first-rate — those by Landowska and Andreï Vieru spring instantly to mind — but no other reading of my experience possesses that uncanny quality of almost preternatural rightness that's the preeminent hallmark of Gould's Bach readings.
Perhaps the most illuminating nontechnical characterization of Bach's keyboard polyphony — illuminating for performer and listener alike — is that, at bottom, it's an in-progress intellectual and philosophic conversation carried on by intellectual equals. And, interestingly, embedded within that anthropomorphic characterization lies, I think, the answer to the question.
While all first-rate keyboardists recognize that in-progress conversation and acknowledge its existence in their Bach readings, Gould alone among them understands precisely what each speaker is saying, knows exactly what the conversation is about, and understands fully all its manifold implications.