(61) Why, when he had begun with Cain, he still mentions him here in the second place, when he says: “And God had respect unto Abel and unto his offerings; but unto Cain and unto his sacrifices he paid no attention?” (#Ge 4:5). In the first place, because the good man, who is by nature first, is not at first perceived by the outward senses of any man except in his own turn, and by people of virtuous conduct. Secondly, because the good and the wicked man are two distinct characters; he accepts the good man, seeing that he is a lover of what is good, and an eager student of virtue; but he rejects and regards with aversion the wicked man, presuming that he will be prone to that side by the order of nature. Therefore he says here with exceeding fitness, that God had regard, not to the offerings, but to those who offered them, rather than to the gifts themselves; for men have regard to and regulate their approbation by the abundance and richness of offerings, but God looks at the sincerity of the soul, having no regard to ambition or illusion of any kind.
(62) What is the meaning of the distinction here made between a gift and a sacrifice? (Genesis 4:4). The man who slays a sacrifice, after having made a division, pours the blood around the altar and takes the flesh home; but he who offers it as a gift, offers as it should seem the whole to him who accepts it. Therefore, the man who is a lover of self is a distributor, like Cain; but he who is a lover of God is the giver of a free gift, as was Abel.
(63) How it was that Cain became aware that his offering had not pleased God? (#Ge 4:5). Perhaps he resolved his doubts, an additional cause being added, for sorrow seized upon him and his countenance fell. Therefore, he took the sorrow which he felt as an indication that he had been sacrificing what was not pleasing or approved of, when joy and happiness would have been suited to one who was sacrificing with purity of heart and spirit.