The yoga postures (Asana) allow us to meditate on the body and gain a profound understanding and knowledge of its nature. Intellectual growth in the mind and strengthening and expansion of neurological connections serve us in the spiritual quest of unity and illumination. Yoga Asana can also be destructive when done without proper guidance of guru or teacher.
Ancient Yogis had a belief that in order for man to be in harmony with himself and his environment, he has to integrate the body, the mind, and the spirit. For these three to be integrated, emotion, action, and intelligence must be in balance. The Yogis formulated a way to achieve and maintain this balance and it is done through exercise, breathing, and Meditation - the three main Yoga structures.