A scientist sets out to conquer nature through knowledge - external nature, external knowledge. By these means he may split the atom and achieve external power. A yogi sets out to explore his own internal nature, to penetrate the atom (atma) of being. He does not gain dominion over wide lands and restless seas, but over his own recalcitrant flesh and febrile mind.
B.K.S. IyengarWe can wash the skin of our bodies with a bath, but through asana practice we not only purify our blood and cells, we are cleansing the inner body as we practice.
B.K.S. Iyengar