Augustine of Hippo : Truly that multitude which was promised to Abraham is not innumerable to God, although it is to the human mind. But to God not even the dust of the earth is so. Further, the promise here made may be understood not only of the nation of Israel but of the whole seed of Abraham, which may be fitly compared with the dust for its multitude. Regarding this seed, there is also the promise of many children, not according to the flesh but according to the spirit. However, the reason why I said that this is not clear from the text is that even the multitude of the one people sprung from Abraham, according to the flesh, through his grandson Jacob, has increased so greatly as to fill almost every region of the world. It is because even the number of this progeny is beyond human power to count that it may, by a hyperbole, be compared with the number of dust particles. What is beyond doubt is that the only land meant is that which is called Canaan. However, some may find a difficulty in the expression "I will give to you and your posterity forever," if the "forever" is taken to mean "eternally." There is no trouble if only they will take this "forever" to mean "to the end of time," which, as we hold on faith, is to be the beginning of eternity. For although the Israelites are expelled from Jerusalem, they still remain in other cities in the land of Canaan and shall remain even to the end. And even when that whole land is inhabited by Christians, they also are the very seed of Abraham. — City of God 16.21 John Chrysostom : Then, in case Abraham should have regard only to his own condition, his advanced years and Sarah's sterility, and thus lose confidence in the promise instead of trusting in the power of the One making the promise, he said, "I will make your descendants as numerous as all the grains of sand in the world. If anyone can number the grains of sand in the world, your descendants too will be numbered." No doubt the promise went beyond human nature. Not only did he promise to make him a father despite so many impediments but also to extend the gift to such a multitude as to be compared with all the grains of sand in the world, and the multitude to be beyond number, wishing as he did to demonstrate the extent of the remarkable increase by the comparison. — HOMILIES ON Genesis 34.10