The Vedic classics describe Yoga as mental rather than a physical discipline. More ritualistic, archaic & orally taught. Yogis talked about MOKSHA the liberation of the spirit by gathering around the holy fire making primordial sounds. People relied on these dedicated rishis who were known for their intensive spiritual practices. There was no need to do teachers training to practice or promote Yoga.
Dhyana the ancient meditation techniques we…re practiced to attain tranquility and the crux of dhyana was to detach from worldly pleasures to connect with the highest state of self realization a transcendental state of SAMADHI. Even the Yog Sutras emphasize PRANAVA the divine word as a prime principle of Yoga practice.
The perception of Yoga now a days has changed significantly. There is less of spiritual and more of physical practices in Yoga. Very small percentage of the curriculum in most Yoga schools deal with spiritual aspects of Yoga. Both the student and the teacher remain deprived of the authentic Yoga the wisdom of our ancient masters.