Yoga teaches us how to control the mind so that it is not thrown out of the balance into wave forms. Yoga is the science that teaches us to stop the Chitta (the mind - stuff) from getting into their changes.
When we think of ourselves it is the body that comes into our imaginations. Training begins with the body itself. Ultimately, they spirit manifest itself. We have to develop different abilities to conquer, it is the science that deals with body, breathe, mind, soul and ultimately the universe itself.