Genesis 21:11

11.And the thing was very grievous in Abraham’s sight. Although Abraham had been already assured, by many oracles, that the blessed seed should proceed from Isaac only; yet, under the influence of paternal affection, he could not bear that Ishmael should be cut off, for the purpose of causing the inheritance to remain entire to him, to whom it had been divinely granted; and thus, by mingling two races, he endeavored, as far as he was able, to confound the distinction which God had made. It may truly seem absurd, that the servant of God should thus be carried away by a blind impulse: but God thus deprives him of judgment, not only to humble him, but also to testify to all ages, that the dispensing of his grace depends upon his own will alone. Moreover, in order that the holy man may bear, with greater equanimity, the departure of his son, a double consolation is promised him. For, first, God recalls to his memory the promise made concerning Isaac; as if he would say, it is enough and more than enough, that Isaac, in whom the spiritual benediction remains entire, is left. He then promises that he will take care of Ishmael, though exiled from his paternal home; and that a posterity shall arise from him which shall constitute a whole nation. But I have explained above, on the seventeenth chapter (Genesis 17:1,) what is the meaning of the expression, ‘The seed shall be called in Isaac.’ And Paul, (Romans 9:8,) by way of interpretation, uses the word reckoned, or imputed. (436) And it is certain that, by this method, the other son was cut off from the family of Abraham; so that he should no more have a name among his posterity. For God, having severed Ishmael, shows that the whole progeny of Abraham should flow from one head. He promises also to Ishmael, that he shall be a nations but estranged from the Church; so that the condition of the brothers shall, in this respect, be different; that one is constituted the father of a spiritual people, to the other is given a carnal seed. Whence Paul justly infers, that not all who are the seed of Abraham are true and genuine sons; but they only who are born of the Spirit. For as Isaac himself became the legitimate son by a gratuitous promise, so the same grace of God makes a difference among his descendants. But because we have sufficiently treated of the various sons of Abraham on the seventeenth chapter, the subject is now more sparingly alluded to.