I was familiar with Iyengar as a style of yoga and have another book, one of the first I ever purchased about yoga, that details poses according to this style. The B.K.S. Iyengar Yoga site has plenty of information about Iyengar’s life and his philosophy of yoga.
One of the many aspects of yoga that I love is simply going through a series of asanas. When my mind is focused and my body glides, I feel graceful and strong, like a dancer. Over my years of practice, my body has kinesthetically learned how to move, how to come into and move out of a pose. I know what my teachers are talking about when they describe a movement and often know some of the Sanskirt names. I love the flow that comes from practice. Here is what Iyengar says about asana:
The asana has to enshrine the entire being of the doer with splendour and beauty. This is spiritual practice in physical form.
Asana means posture, which is the art of positioning the body as a whole with a physical, mental and spiritual attitude. Posture has two aspects, namely posing and reposing. Posing means action. Pose is assuming a fixed position of limbs and body as represented by the particular asana being performed. Reposing means reflection on the pose. The pose is re-thought and readjusted so that the various limbs and parts of the body are positioned in their places in a proper order and feel rested and soothed, and the mind experiences the tranquility and calmness of bones, joints, muscles, fibres and cells.
Prana is energy. Ayama is creation, distribution and maintenance. Pranayama is the science of breath, which leads to the creation, distribution and maintenance of vital energy.
Any asana done on an inhalation will end in merely physical action, whereas an asana done on an exhalation is vital and organic, and produces physiological action and cellular health.