Sarah, in fact, was barren; and, despairing of offspring, and being resolved that she would have at least through her handmaid the blessing she saw she could not obtain in her own person, she gave her handmaid to her husband, to whom she herself had been unable to bear children. From him she required this conjugal duty, exercising her own right in another's womb. And thus Ishmael was born according to the common law of human generation, by sexual intercourse. Therefore it is said that he was born “according to the flesh,”— not because such births are not the gifts of God, nor His handiwork, whose creative wisdom “reaches,” as it is written, “from one end to another mightily, and she orders all things sweetly,”⁠a but because, in a case in which the gift of God, which was not due to men and was the free gift of grace, was to be conspicuous, it was necessary for a son to be given in a way that no effort of nature could achieve. Nature denies children to persons of the age which Abraham and Sarah had now reached; and besides, in Sarah's case, she was barren even in her prime. This nature, so constituted that offspring could not be looked for, symbolized the nature of the human race corrupted by sin and justly condemned as a result, which deserves no future happiness. Fittingly, therefore, Isaac, the child of promise, prefigures the children of grace, the citizens of the free city, who dwell together in everlasting peace, in which self-love and self-will have no place, but where a serving love that rejoices in the common joy of all makes one heart out of many, that is to say, secures a perfect concord.