Yoga is an ancient tradition developed for the purpose of self development.
Its primary goal is to develop awareness, discrimination and clarity. Yoga provides a practical and wholistic way to go about this development. The practice of physical yoga postures provides us with a direct experience of change and expanded possibilities. Whilst these occur on a body level, it is only by changing the mind, or using the mind in another way that we are able to develop our adoption of a physical posture. There is a lot of good literature concerning yoga, should you wish to pursue the theory more thoroughly.