John Chrysostom

Do you observe that this was ordered by Providence from of old? What then, he means, does He say this on account of the Ishmaelites, or of the Amalekites, or of the Hagarenes? This however, as he goes on he proves more distinctly not to be said of these. But as yet he presses forward to another point, by which means he proves this very thing by defining the mode of the relationship, and establishing it with a vast reach of mind.

But his meaning is something of this sort, as God is not the God of a part, but the Father of all, so is he also. And again, as God is a father not by way of the relationship of nature, but by way of the affiance of faith, so is he also inasmuch as it is obedience that makes him father of us all. For since they thought nothing of this relationship, as clinging to that grosser one, he shows that this is the truer relationship by lifting his discourse up to God. And along with this he makes it plain that this was the reward of faith that he received. Consequently, if it were not so, and he were the father of all the dwellers upon earth, the expression before (or answering to) would be out of place, while the gift of God would be curtailed.

For if He could "quicken the dead" and bring in "those things that were not as though they were," then could He also make those who were not born of him to be his children. And this is why he does not say, bringing in the things which are not, but calling them, so showing the greater ease of it. For as it is easy to us to call the things which are by name, so to Him it is easy, yea, and much easier to give a subsistence to things that are not.