The soul is something which contains the body. The body doesn't contain the soul. The soul, if we put it into modern language, is the entire complex of relationships in whose context this organism exists.
For I did not know that the soul needs to be enlightened by light from outside itself, so that it can participate in truth, because it is not itself the nature of truth.
Nothing is more stimulating and more salutary to (or for) the inner (or inward) development than the exemple of men devoted to the good. It is in the company of men pursuing a same ideal that the still weavering (or unsteady) soul can set oneself ("se fixer", Fr) and stick to (or attach to) everything that is noble and generous.