When you experience everything as oneness in your consciousness, then you are in yoga. To attain that unity within you, there are many ways. You work with the body, then you move to the breath, then to the mind, then to the inner self. Like this, many steps have been created, but they are only different facets of yoga. It is important that all of them are addressed in a very balanced way, all at once, as one single unit. There is really no division as such; yoga employs all aspects of who you are.
The body is a very large part of who you are right now. The science of using the body to hasten your evolutionary process is hatha yoga. The body itself has its own attitudes, its own ego, its own nature. Let us say you decided, “Starting tomorrow, I will get up at five in the morning and go for a walk.” You set the alarm. The alarm rings. You want to get up, but your body says, “Shut up and sleep.” It has its own way, doesn’t it? Hatha yoga is a way of working with the body, a way of disciplining, purifying and preparing the body for higher levels of energy and possibilities.