The soul and the body are two opposites, one pulling toward G-d and one pulling away from him. Originally, the soul had the strength to lift up the body and purify it. After Adam's sin, the soul is given with a certain lack such that it cannot overpower the body and the body has just as much strength to pull down as the soul has to pull up. The aim of this world is to purify the body while being distracted by the evil inclination. If Adam had not sinned, he would have witnessed the change in his body and the entire Gan Eden around him. Now, we must fight our desires to be able to purify our bodies in this world so that we're able to achieve the World to Come.