These hostile manifestations invariably make their appearance after the teacher has made an appearance anywhere. Light must inevitably cast a shadow. Yet on the credit side they served a useful purpose. They help him and they help his probationers. They remind him that he must not stake a claim on any part of this earth's surface or in any human heart. They test the intuition and keenness of the probationers. When these have survived all the tests, he may accept them and begin their real inner work together; thereafter God himself cannot prize them apart from their teacher, for then they know with whom they are dealing.
-- Notebooks Category 11: The Negatives > Chapter 2: Their Roots in Ego > # 64