Section 31: Reverence Without Superstition explained simply

XXXI. As to piety towards the gods you must know that this is the chief thing, to have right opinions about them, to think that they exist, and that they administer the All well and justly; and you must fix yourself in this principle (duty), to obey them, and to yield to them in everything which happens, and voluntarily to follow it as being accomplished by the wisest intelligence. For if you do so, you will never either blame the gods, nor will you accuse them of neglecting you. And it is not possible for this to be done in any other way than by withdrawing from the things which are not in our power, and by placing the good and the evil only in those things which are in our power. For if you think that any of the things which are not in our power is good or bad, it is absolutely necessary that, when you do not obtain what you wish, and when you fall into those things which you do not wish, you will find fault and hate those who are the cause of them; for every animal is formed by nature to this, to fly from and to turn from the things which appear harmful and the things which are the cause of the harm, but to follow and admire the things which are useful and the causes of the useful. It is impossible then for a person who thinks that he is harmed to be delighted with that which he thinks to be the cause of the harm, as it is also impossible to be pleased with the harm itself. For this reason also a father is reviled by his son, when he gives no part to his son of the things which are considered to be good; and it was this which made Polynices and Eteocles enemies, the opinion that royal power was a good. It is for this reason that the cultivator of the earth reviles the gods, for this reason the sailor does, and the merchant, and for this reason those who lose their wives and their children. For where the useful (your interest) is, there also piety is. Consequently he who takes care to desire as he ought and to avoid ([Greek: echchlinein]) as he ought, at the same time also cares after piety. But to make libations and to sacrifice and to offer first-fruits according to the custom of our fathers, purely and not meanly nor carelessly nor scantily nor above our ability, is a thing which belongs to all to do.