Body is the bow, asana the arrow, and the soul the target

"No doubt, one may say reading holy books is spiritual practice. But what I teach is spiritual practice in action. I use the body to discipline the mind and to reach the soul. Asanas, when done with the right intention, will help to transform the individual by taking the person away from an awareness of just the body toward the consciousness of the soul. Indeed, as I often say, body is the bow, asana the arrow, and soul is the target." 

~ BKS Iyengar, Light on Life