Yoga is a subject about education about oneself. it is a mirror for understanding oneself. We are supposed to be knowers of the ksetra [field] which is our sarira [very loosely translated as body]. The body in this case is not what the anatomists and physiologists study. It includes the gross [sthula], sukshma [subtle] and karana [causal]. Yoga is a pursuit to know our embodiment which has several layers from the annamaya, pranamaya, monamaya, vijnanamaya and finally the anandamaya. On the grosser plane, our embodiment is the body, mind and breath. We have to study how they interact, interplay and interface with each other. He then guides us practically in an asana on how to have a profound interaction between the body, mind and breath so that we no longer DO yoga but yoga happens on us!