A reader brought attention to an old post of mine that might bear re-posting here, specifically this quote from Sullivan about the Master:
“An inner life of quite extraordinary intensity was in process of development till the very end. Other artists, of those few whose spirits were both sensitive and free, seem to have passed through similar stages of development. But perhaps even Shakespeare never reached that final stage of illumination that is expressed in some of Beethoven’s late music. The other steps of the journey he knew, but Shakespeare never wrote his C-sharp-minor quartet. It is possible, indeed, that Beethoven’s late music is unique, not only in music, but in the whole of art.”