The divine law is unknown to the soul that folly and intemperance have rendered impure, but it shines forth in self-control and wisdom. It is impossible to transgress this, for there is nothing in man that can transcend it. Nor can it be despised, for it cannot shine forth in a man who will despise it. Nor is it moved by chances of fortune, because it is in truth superior to chance and stronger than any form of violence.
Mind alone knows it, and diligently pursues the search thereafter, and finds it imprinted in itself, and supplies from it food to the soul as to its own body. We must regard the rational soul as the body of the mind, which the mind nourishes by bringing into recognition, through the light that is in it, the thoughts within, which mind imprinted and engraved in the soul in accordance with the truth of the divine law. Thus mind is become teacher and savior, nurse, guardian and leader, speaking the truth in silence, unfolding and giving forth the divine law; and looking on the impressions thereof in itself it beholds them implanted in the soul from all eternity.
You must therefore first understand the law of nature, and then proceed to the divine law, by which also the natural law has been prescribed. And if you make these your starting-point you shall never fear the written law. For written laws are made for the benefit of good men, not that they may do no wrong, but that they may not suffer it. Natural wealth is limited, and it is easy to attain. But the wealth desired of vain opinions has no limits, and is hard to attain.
The true philosopher therefore, following nature and not vain opinions, is self-sufficing in all things; for in the light of the requirements of nature every possession is some wealth, but in the light of unlimited desires even the greatest wealth is but poverty. Truly it is no uncommon thing to find a man who is rich if tried by the standard of vain opinions. No fool is satisfied with what he possesses; he rather mourns for what he has not. Just as men in a fever are always thirsty through the grievous nature of their malady, and desire things quite opposed to one another, so men whose souls are ill-regulated are ever in want of all things, and experience ever-varying desires through their greed."
— Porphyry, Letter to Marcella