Health is a state of complete harmony of the body, mind and spirit. When one is free from physical disabilities and mental distractions, the gates of the soul open.
The practice of yogasana for the sake of health, to keep fit, or to maintain flexibility is the external practice of yoga. While this is a legitimate place to begin, it is not the end. Even in simple asanas, one is experiencing the three levels of quest: the external quest, which brings firmness of the body; the internal quest, which brings steadiness of intelligence; and the innermost quest, which brings benevolence of spirit.
Health is a state of complete harmony of the body, mind and spirit.
When your body, mind and soul are healthy and harmonious, you will bring health and harmony to the world- not by withdrawing from the world, but by being a healthy, living organ of the body of humanity.
Look after the root of the tree, and the fragrant flower and luscious fruits will grow by themselves. Look after the health of the body, and the fragrance of the mind and richness of the spirit will follow.
As long as the body is not in perfect health, you think about it, and that prevents you from thinking of the mind. The sound mind is a sound body.