The play suggests, and quite reasonably in my opinion, that Schubert believed that the Beethoven quartet would cure him of his terminal syphillis. The play cleverly interweaves a commentary by the performers of the piece (the Coull Quartet) with the dramatization giving a simultaneous musicological and dramatic flavor to the performance.
It works very well as a play, but in truth the music, even played only as excerpts in this case, simply overwhelms the drama. The spiritual power of Beethoven manifested in this (and the other late quartets) is as direct a route to God (or the transcendent stream of life) as you will find. No wonder Schubert craved a performance before his death - one can only hope that the performance eased his passage into the afterlife. I suspect it did.