God placed for every son of Adam seven castles, inside of which is Himself and outside of which is Satan barking like a dog. When man allows a breach to be opened in one of them, Satan enters through it. It is to be advised, then, that he guard and keep watch over them with all care, particularly the first castle; for while their foundations remain healthy and while they are still standing, there is no evil to fear.
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Originally published as “Teresa of Jesus and Islam: The Simile of the Seven Concentric Castles of the Soul,” in A New Companion to Hispanic Mysticism. Brill, 2010. Republished here with thanks to the publisher.