The True Nature of Health by B.K.S. Iyengar

Ofspirit.com has a nice excerpt from BKS Iyengar's new book "Light on Life".
Link

The True Nature of Health
by B.K.S. Iyengar
Most people ask only from their body that it does not trouble them. Most people feel that they are healthy if they are not suffering from illness or pain, not aware of the imbalances that exist in their bodies and minds that ultimately will lead to disease. Yoga has a threefold impact on health. It keeps healthy people healthy, it inhibits the development of diseases, and it aids recovery from ill health.

But diseases are not just a physical phenomenon. Anything that disturbs your spiritual life and practice is a disease and will manifest eventually in illness. Because most modern people have separated their minds from their bodies and their souls have been banished from their ordinary lives, they forget that the well-being of all three (body, mind, and spirit) are intimately entwined like the fibers of our muscles.

Health begins with firmness in body, deepens to emotional stability, then leads to intellectual clarity, wisdom, and finally the unveiling of the soul. Indeed health can be categorized in many ways. There is physical health, which we are all familiar with, but there is also moral health, mental health, intellectual health, and even the health of our consciousness, health of our conscience, and ultimately divine health. These are relative to and depend upon the stage of consciousness we are at, which will be dealt with in chapter 5."