The piece is not quite as difficult as it sounds. The staggering of many notes make it sound much faster than it really is. And the many long notes alleviate some difficulties by providing opportunities for rest, and thus opportunity for concentration to be focused on the other two parts.The long notes, traveling through the voices adds much to the harmony and texture, and greatly enhances the overall effect.
It was a little different than what one associates with a fugue but that makes it all the more interesting.
I'm glad to know that a church might be a better listening experience than a cathedral for the pipe organ. St. John's Episcopal church in neighboring Olympia has just installed a Hermann Schlickter pipe organ. It looks quite massive in the article pictures.