"Shariramadyam khalu dharma Sadhanam."
"The first duty is to take care of the body, which is the means to the pursuit of the spiritual life."
"Nayam ama balahinena labhyah"
"This Self cannot be gained by one devoid of strength."
These quotes from the Upanishads (ancient Yogic scriptures) are just two of the many insistences upon the connection between a healthy body and spirit in Yogic theory. Without a healthy, strong body and an unclouded, peaceful mind, no progress on the spiritual path can be made. This is why commitment to daily asana practice and other kriyas (actions that cleanse the physical body) were so central to the teachings of yoga. It's not that improvement of the body itself was important, but in cleansing and strengthening the physical self, you remove the obstacles that are preventing you from advancing in your spiritual growth.
The ways in which our bodies reflect our mental/emotional/spiritual state and vice versa are innumerable. Yogis, scholars ad scientists have been studying this since the beginning of time, as understanding and being able to harness the knowledge of this intricate intertwinement is THE secret to a life well lived.
I'm not saying that BOOM I get heart surgery and all of a sudden I gain enlightenment, but I am excited to see what effects this jolt of physical improvement will have on my spiritual progression. It's probably good that I feel this way or I'd just be scared shitless...
What sort of negative thoughts are causing you sickness or what sort of physical self-abuse (poor eating, lack of sleep, etc.) are limiting your spiritual growth? It's certainly worth thinking about. In fact, I can't imagine anything else that is more worthy of our contemplation.