I know that when I first encountered yoga as a spiritual practice, the question in my mind was: What does exercising this body have to do with spirituality? The soul exists in the realm of the spiritual, yes, but it also exists in this world through a container or a vehicle, the physical body. If the vehicle is broken, uncovering the soul would be difficult because all energy would be spent on fixing the vehicle. In the same manner, if the vehicle is operating in tip top shape, the machine is maintained very well, the vehicle can do its work of transporting the soul.
Of all the physical exercises that I’m aware of, it’s only yoga practices that acknowledge both the body and the soul. And it is because of the recognition of the existence of both that the approach to the physical body is nurturance over obsession, conditioning over attachment, practice over perfection. We acknowledge that we keep this body in shape not because the end goal is to keep the body in shape, the end goal is to delve into the soul.