Your body wants to eat, to sleep, to lust. Your soul wants things that have permanence. These opportunities for real accomplishment generally require effort to achieve. Your bodily desires, on the other hand, have nothing to do with the future. They seek satisfaction for the moment.
Desire is for the moment.
It's an escape. Want is for permanence. It's rooted in reality. For example, you want to take the final exam, but you don't feel like it. It's not easy to win out over your desires.