Knowledge of God is Necessary for Virtue
Taught of God himself what goodness is, we have both a perfect knowledge of it as revealed to us by a perfect Master; and faithfully we do His will, as enjoined on us by a Judge we dare not despise. But your ideas of virtue you have got from mere human opinion; on human authority, too, its obligation rests: hence your system of practical morality is deficient, both in the fulness and authority requisite to produce a life of real virtue. Man’s wisdom to point out what is good, is no greater than his authority to exact the keeping of it; the one is as easily deceived as the other is despised.
Though withal you know that these very laws also of yours, which seem to lead to virtue, have been borrowed from the law of God as the ancient model. Of the age of Moses we have already spoken. But what is the real authority of human laws, when it is in man’s power both to evade them, by generally managing to hide himself out of sight in his crimes, and to despise them sometimes, if inclination or necessity leads him to offend? Think of these things, too, in the light of the brevity of any punishment you can inflict—never to last longer than till death.
–Apology ch. 45