The body is there because the mind seeks desires through the body; desires cannot be fulfilled without the body. You can be completely fulfilled without the body, but desires cannot be fulfilled without the body. Desire needs the body; the body is the vehicle of desire. That's why possession happens. You have heard, you must have heard, many stories about a ghost possessing somebody else. Why is a ghost so interested in possessing somebody else? It is because of desires. Desires cannot be fulfilled without a body, so he enters somebody's body to fulfill his desires.