B.K.S. Iyengar is one of the most well-known yoga teachers in the world. He is as responsible as anyone for making yoga the phenomenon it is in the west. In his younger days, his amazing ability to contort his body fascinated people around the world, and as he taught the precise and detailed poses (or asanas), he helped to spread the news of yoga's healthy benefits. His guide, Light on Yoga, is a classic of Hatha Yoga which shows and describes scores of yoga asanas.
To Iyengar and other Yogis, Yoga is much more than a type of exercise; it encompasses life in all aspects: physical, emotional, intellectual and spiritual. To make this point, Iyengar wrote Light on Life as a guide to the other aspects of yoga. Subtitled "The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom," Light on Life describes how the physical asanas move the yoga practitioner toward a kind of enlightenment. Each asana is designed not only to improve physical health; it is also designed to help the student come to know herself better. Self-knowledge then leads one on a path of understanding until finally inner peace and ultimate freedom are achieved.
Like all such books that describe a path to enlightenment, inner peace, or whatever they call it, the book is more a set of way markers than a step-by-step guide. Still, Iyengar describes the process as moving from the physical body in asanas to the energy body, the mental body, the intellectual body and ultimately, the divine body. Each step is not discrete, however--we always have all these bodies, but how aware of them we are differs depending on our practice, our ability, our devotion, as well as effects that are out of our control.
As one who is not very far advanced in the ways of yoga, I can't tell you if this book will get you to inner peace and ultimate freedom. Parts of it are difficult to follow and understand, but such ideas may become more clear as I progress on the journey. In any case, Iyengar's book is worth reading if you are at all interested in the more spiritual aspects of yoga.