"Under the plea that it is impossible not to sin, they are given a false sense of security in sinning ... Anyone who hears that it is not possible for him to be without sin will not even try to be what he judges to be impossible, and the man who does not try to be without sin must perforce sin all the time, and all the more boldly because he enjoys the false security of believing that it is impossible for him not to sin ... But if he were to hear that he is able not to sin, then he would have exerted himself to fulfil what he now knows to be possible when he is striving to fulfil it, to achieve his purpose for the most part, even if not entirely."

“Whenever I have to speak on the subject of moral instruction and the conduct of a holy life, it is my practice first to demonstrate the power and quality of human nature.”

“Yet we do not defend the good of nature to such an extent that we claim that it cannot do evil, since we undoubtedly declare also that it is capable of good and evil; we merely try to protect it from an unjust charge, so that we may not seem to be forced to do evil through a fault of our nature, when, in fact, we do neither good nor evil without the exercise of our will and always have the freedom to do one of the two, being always able to do either.”

“When will a man guilty of any crime or sin accept with a tranquil mind that his wickedness is a product of his own will, not of necessity, and allow what he now strives to attribute to nature to be ascribed to his own free choice? It affords endless comfort to transgressors of the divine law if they are able to believe that their failure to do something is due to inability rather than disinclination, since they understand from their natural wisdom that no one can be judged for failing to do the impossible and that what is justifiable on grounds of impossibility is either a small sin or none at all.”

“Love of wealth is insatiable, desire for honour knows no fulfilment; possessions destined to meet with a speedy end are sought endlessly. But divine wisdom, heavenly riches, immortal honours we neglect in our indifference and sloth, and, as for spiritual riches, either we do not touch them at all or, if we get a slight taste of them, we at once suppose that we have had enough. The divine Wisdom invites us to its feasts in quite different terms: Those who eat me, she says, will hunger for more, and those who drink me will thirst for more . No one can have enough of such feasts or ever suffers from squeamishness because he has had too much: the more he drinks from that source the greater will be each man's capacity and eagerness for more.”

“It was because God wished to bestow on the rational creature the gift of doing good of his own free will and the capacity to exercise free choice, by implanting in man the possibility of choosing either alternative. ... He could not claim to possess the good of his own volition, unless he was the kind of creature that could also have possessed evil. Our most excellent creator wished us to be able to do either but actually to do only one, that is, good, which he also commanded, giving us the capacity to do evil only so that we might do His will by exercising our own. That being so, this very capacity to do evil is also good – good, I say, because it makes the good part better by making it voluntary and independent, not bound by necessity but free to decide for itself.”

“If you depart from evil but fail to do good, you transgress the law, which is fulfilled not simply by abominating evil deeds but also by performing good works.”