(58) Why does the divine oracle, in the way of intimation, say to Abraham, Yes, be it so: behold Sarah thy wife shall also bring forth a son unto thee? (#Ge 17:19). The meaning of this sentence is as follows: that confession and admission, says God, is on my part an admission of thy wish, being manifestly full of unadulterated joy; and your faith is not doubtful, but without any hesitation it has a share of modest awe and reverence; therefore that which thou hast received before, as to be done unto thee on account of thy faith in me, shall certainly be done; for this is what is meant by yes.
(59) Why does he say, But behold I will also listen to thee concerning Ishmael, and I will bless him, and he shall become the father of twelve nations? (#Ge 17:20). God says, I will grant to thee both the first and the second blessing, that is to say, both the blessings of nature and the blessings of instruction; by nature that which is according to the legitimate course of nature, that is Isaac, and by instruction that which is according to Ishmael, who is not legitimate: for hearing, when compared with sight, is like the illegitimate compared with the legitimate, and what is brought about by instruction is not of the same class with that which owes its existence to nature; and the man who is desirous of encyclical wisdom becomes the father of nations, for the encyclical number is a period of twelve days and years.
(60) Why does he say, But I will set up my covenant with Isaac, whom Sarah shall bring forth about this time in the succeeding year? (#Ge 17:21). As in men’s wills some persons are set down as heirs, and some are entered as worthy of gifts which they are to receive from the heirs, so also in the divine testament that man is set down as the heir who is by nature a worthy disciple of God being adorned with all perfect virtues; but he who is introduced by learning, and is made subject to the law of wisdom, and partakes in encyclical instruction, is not at all an heir, but only a receiver of gifts gratuitously given. But it is said with great wisdom and propriety that his mother shall bring forth Isaac in the succeeding year, since this birth unto life does not belong to the present time, but to another great and holy time; and that which is divine rejoices in excessive abundance, and is by no means like the nations of this world.