Against Marcion 2.18

But what good things of the law should I defend rather than those which the heresy has been eager to shake? Such as the rule of retaliation, which demands eye for eye, tooth for tooth, and bruise for bruise. It does not savour of a licence to inflict injury in turn, but looks to restraining violence altogether. To a people most hard and unfaithful toward God it would have seemed a long wait, or even incredible, to expect vindication from God, which was later to be proclaimed through the prophet: “Vengeance is mine, and I will repay, says the Lord.” Meanwhile, therefore, the committing of injury was to be checked by fear of a requital that would meet it at once, and the licence to retaliate was to be a prohibition of provocation, so that wickedness might cease, made safe from itself: while the second blow is permitted, the first is deterred, and when the first is deterred, the second is not struck either — since in other respects too the fear of retaliation works more readily through a taste of the same suffering. Nothing is more bitter than to suffer the very thing you have done to others.

And if the law takes something away from food and declares unclean animals that were once blessed, understand the plan of exercising self-control, and recognize the reins put on that gluttony which, while eating the bread of angels, longed for the cucumbers and melons of the Egyptians. Recognize too that provision was made against gluttony's companions, lust and luxury, which generally cool when the belly is disciplined — for “the people ate and drank and rose up to play.” Likewise, so that the craving for money might also be quenched in part, where it pleads the necessity of food, the ambition for costly foods was taken away. Lastly, so that man might more easily be trained to fast for God, he was accustomed to few and unglamorous foods, so as not to go hungry for any of the more luxurious. The Creator is surely to be blamed for taking foods away from his own people rather than from the more ungrateful Marcionites! Nor let anyone blame the burdens of sacrifices and the fussy scrupulousness of rituals and offerings, as though God had desired such things for himself, when he so plainly cries out: “What to me is the multitude of your sacrifices?” and “Who has required these things from your hands?” Rather, let him perceive God's careful purpose, by which he wished to bind a people prone to idolatry and transgression to his own religion by duties of the kind in which the superstition of the world was carried on, so as to call them away from it — commanding that these things be done to himself, as though he desired them, lest they sin by doing them for images.