As the Body is for the Purusha,
So are Asanas for Yoga
Misconceptions about Asana Practice
The body existing for the sake of the Purusha
In the Yoga Sutras, there are two sutras where Patanjali makes it very clear that the body exists solely for the purpose of the Purusha (Atma) to provide it with experience (enjoyment) and act as a vehicle for liberation. Patanjali, in Sutra 2.18, uses the words "Bhoga Apavargartham Dhrishyam", where Bhoga means experience and Apavarga means liberation, the two purposes that the body serves the Purusha for. In Sutra 2.21 (shown below), he says that the Prakriti (which includes the body) exists solely for the sake of the Seer, the Purusha.
The body gives structure for the Purusha to express itself. The Purusha after accomplishing its desires in a lifetime, gives up the body and takes on a new one, according to the philosophy of yoga and its sister philosophy Sankhya (the path of knowledge). This is beautifully expressed in Shloka 2.22 in the Bhagavad Gita
The Purusha and the Prakriti
Asanas are meant to serve the person
T. Krishnamacharya, known as the father of modern day yoga, would say that the asanas are meant to serve a person and not the other way around. Quite unfortunately, in some modern day yoga schools, most notably schools which follow a rigid sequence like Ashtanga Vinyasa Yoga, this is turned around, with the expectation from some teachers that one strictly adhere to the sequence and if one is not able to perfect a pose, is then not allowed to go past that pose to do the succeeding pose in the sequence. Sometime back, I attended a Ashtanga Yoga workshop and the first instruction in the "welcome letter" was 'Do not skip any asana'. Though the instructor, a very experienced practitioner who understood yoga well beyond asanas, did not care for these rules, the organizer did.
Invariably every long time asana practitioner who is familiar with some level of the yoga philosophy understands this -that these asanas are just a tool for us to experience those deep states of mind and refined feelings (Vedana). That is the end purpose of the asanas. They have no more sanctity.