In the past the mind commanded the body without trouble, and the body obeyed freely and willingly. Now, with the natural order of things disturbed [through the fall of man], the passions of the body seek to override the reason... .
Man, hampered as he is by this perplexing division, may be compared to an unruly state. Such a state is composed of various sorts of men whose dissensions create frequent disturbances and factions. To prevent strife the greatest power must be given to one supreme authority, and this authority must be of such a nature that it commands nothing that is not for the welfare of the state.
In man, reason discharges the office of king. [...] Consider the dregs of the lower classes to be those affections or passions that dissent as much as possible from the decrees of reason and that are least humble. These are lust, lechery, envy, and similiar diseases of the mind, which we ought to resist as overseers restrain dirty, vile slaves so as to ensure that they perform the tasks assigned them by the master, or, at least, so as to prevent them from doing harm. The divinely inspired Plato wrote of all these things in his Timaeus.
Though our king, reason, may at times be oppressed, he cannot be corrupted without protesting. He will be able to recover because of the eternal law that has been divinely engraven upon him. [...] ... the Stoics and the Peripatetics... both agree that we should be guided by reason rather than by passion. ...they contend that the truly wise man must be free of all passions of this sort as diseases of the mind. [...] Socrates, in the Phaedo of Plato, appears to agree with the Stoics when he says that philosophy is nothing more than a meditation upon death, that is, a withdrawal of the mind, as much as possible, from corporal and sensible things, and a dedication to those things that can be perceived only by reason. [...] Socrates' fable of the good and the bad charioteers and the good and bad horses is no old wives tale.
This then is the only road to happiness: first, know yourself; do not allow yourself to be led by the passions, but submit all things to the judgement of reason. Be sane and let reason be wise, that is, let it gaze upon decent things.