The Buddha found the religious world of his day, the 6th c. B.C., to be one of pure dogma, book knowledge, and obscure rules. The Indian religious environment was ossified, ritualised, caste-based, sacrifice-ridden, and heavy on the worship of powerful gods. Further, society believed its welfare derived more from the Brahmin's correct performance of rituals than on the gods themselves. The Buddha came from eastern India, in a time of reactions against the ruling priestly class and slaughter of animals, in favor of more ascetic ideals of insight into oneself. He revived a pre-Vedic, non-theistic tradition, and, as a result of his popularity,meditation became the main form of spiritual practice on the entire subcontinent. A thousand years later, around the 5th c. A.D., as was the case with the Shaolin monks (see other post), some Indians began to dispute that you can start meditation without preparing oneself physically. They culled yoga out of its tantric roots, and made it center on purifying the body and its elements. This was codified most completely in the book Hatha Yoga Pradipika, (15th c. A.D.) concluding that before yoga can be acheived, or meditation, the whole body - stomach, intestines, nervous system, etc., or, more specifically, its subtle energy channels- must be purified. In other words, the mind (that herd of wild horses/monkeys) is too unruly to be controlled by the mind, but only by the body - which we can control. Nevertheless, those physical purification techniques require a determined, lengthy commitment, and profound dedication in and of themselves.
Swami Muktibodhananda's commentary on verse 77, chapter 3, H.Y.P:
Enlightenment...has never been interpreted in a religious fashion in the tantric tradition. It has always been known as a physiological possibility which can be induced within the body by certain practices. This is why in the tantric system, as opposed to religious philosophies, purification of the body...is considered a prerequisite for enlightenment. If the body is loaded with toxic elements...or the five chakras are not purified, then enlightenment can not occur.