Pranayama teaches the aspirant to regulate his breathing and thereby control the mind.
B.K.S. IyengarWhile doing the postures, your mind should be in half-consciousn ess, which does not mean sleep. It means silence, emptiness, space, which can then be filled with an acute awareness of the sensations given by the posture. You watch yourself from inside. It is a full silence.
B.K.S. IyengarBy drawing our senses of perception inward, we are able to experience the control, silence, and quietness of the mind.
B.K.S. IyengarThe practice of yogasana for the sake of health, to keep fit, or to maintain flexibility is the external practice of yoga. While this is a legitimate place to begin, it is not the end. Even in simple asanas, one is experiencing the three levels of quest: the external quest, which brings firmness of the body; the internal quest, which brings steadiness of intelligence; and the innermost quest, which brings benevolence of spirit.
B.K.S. Iyengar