Hatha Yoga Pradipika - 3rd Reprint 2016 by Swami Vishnudevananda, Yogi Svatmarama
The purpose of the practice of Yoga is to give your life a boost, to put your spiritual progress in first gear. Then you may go into second gear and maybe into third gear where you can cruise comfortably after climbing the hills. This is unlike most worldly people who just coast downhill without knowing about brakes, thinking that happiness is somewhere down there, waiting. They go straight downhill, faster and faster into numerous disasters such as cancer, AIDS, high blood pressure, heart trouble. Soon it is too late and they crash. So even though it may seem very easy, please don