Genesis 11:30

30.But Sarai was barren. Not only does he say that Abram was without children, but he states the reasons namely, the sterility of his wife; in order to show that it was by nothing short of an extraordinary miracle that she afterwards bare Isaac, as we shall declare more fully in its proper place. Thus was God pleased to humble his servant; and we cannot doubt that Abram would suffer severe pain through this privation. He sees the wicked springing up everywhere, in great numbers, to cover the earth; he alone is deprived of children. And although hitherto he was ignorant of his own future vocation; yet God designed in his person, as in a mirror, to make it evident, whence and in what manner his Church should arise; for at that time it lay hid, as in a dry root under the earth.