Philosophical training puts much value on the quality of mental calmness, emotional composure, and on its reflected state in the body--physical stillness. The more a man's mind is self-composed, the more will his whole personality be self-possessed. The passions of hatred, greed, lust, and anger cannot then blind him to the truth about his human situation or about the world's nature. The bodily postures prescribed by the yoga system of physical control serve their highest purpose, and fulfil their ultimate intention, when they train a man in the art of being perfectly still. For such a man will gradually transfer some of the body's outer quietude to the mind's inner stillness. But he will do so only if properly instructed by book or teacher or correctly guided from within.
-- Notebooks Category 5: The Body > Chapter 5: Exercise > # 82