It's like this, I think: the excellence of a good body doesn't make the soul good, but the other way around: the excellence of a good soul makes the body as good as it can be.
PlatoAll soul is immortal. For that which is always in movement is immortal; that which moves something else, and is moved by something else, in ceasing from movement ceases from living. So only that which moves itself, because it does not abandon itself, never stops moving. But it is also source and first principle of movement for the other things which move.
Plato