(65) What is the meaning of the expression: “You have done wrongly; now rest?” (#Ge 4:8). He is here giving very useful advice; since, to do no wrong at all is the greatest of all good things: but he who sins, and who thus blushes and is overwhelmed with shame, is near akin to him, being, if I may use such a phrase, as the younger brother to the elder; for those persons who pride themselves on their errors as if they had not done wrong, are afflicted with a disease which is difficult to cure, or rather which is altogether incurable.
(66) Why he seems to be giving what is good into the hand of a wicked man, when he says, “And unto thee shall be his desire?” (#Ge 4:8). He does not deliver good into his hand; but the expression is heard with different feelings; since he is speaking, not of a pious man, but after the action is accomplished, saying of him: The desire and respect of the impiety of this man’s wickedness will be towards you. Do not therefore talk about necessity, but about your own habits, in order that thus he may represent the voluntary action. And again, the sentence, “And you shall be his ruler over him,” has a reference to the operation. In the first place, you begin to act with wickedness; and now behold, another iniquity follows that great and injurious iniquity. Therefore, he both thinks and affirms that this is the principal part of all voluntary injury.
(67) Why he slew his brother in the field? (#Ge 4:9). That as all in fecundity and sterility arises from a neglect of sowing and planting land a second time, he may be kept continually in mind of his wicked murder, and self-blamed for it; since the ground was not to be the same for the future, after it was compelled, contrary to its nature, to drink of human blood, to bring forth food to that man who imbued it with the polluted stain of blood.