I own (and have mostly read) Maimonides' The Guide For The Perplexed. The statement that Ganz quoted, though, may not be from that book; I couldn't find it there.
Though I couldn't track down the Maimonides' quote, I was delighted to find another book, right next to The Guide For The Perplexed: The Fire We Can Light, by Martin E. Marty, Professor Emeritus at the University of Chicago Divinity School. That book is one of my favorites, and appears to be out of print. Here is how it begins:
When the Baal Shem had a difficult task before him, he would go to a certain place in the woods, light a fire and meditate in prayer - and what he had set out to perform was done. When a generation later the "Maggid" of Meseritz was faced with the same task he would go to the same place in the woods and say: We can no longer light the fire, but we can still speak the prayers - and what he wanted done became a reality. Again a generation later Rabbi Moshe Leib of Sassov had to perform this task. And he too went into the woods and said: We can no longer light a fire, nor do we know the secret meditations belonging to the prayer, but we do know the place in the woods to which it all belongs - and that must be sufficient; and sufficient it was. But when another generation had passed and Rabbi Israel of Rishin was called upon to perform the task, he sat down on his golden chair in his castle and said: We cannot light the fire, we cannot speak the prayers, we do not know the place, but we can tell the story of how it was done. And ... the story which he told had the same effect as the actions of the other three.
Hasidic tale retold by Gershom G. Scholem