John Chrysostom, on Gen 17:1

“And after he began to be ninety and nine years old, the Lord appeared to him: and said unto him: I am the Almighty God: walk before me, and be perfect.”

“After the tenth year he took Ishmael, his child by the maidservant, and considered that the promises had been fulfilled for him in the child. The patriarch was, you remember, the text tells us, eighty-six years old when Ishmael was born. The loving God, however, exercised the virtue of the just man for a still further period of thirteen years. When God saw that he had been purified like gold in a furnace for a long period of time and had rendered the just man's virtue more conspicuous and resplendent, Scripture says, "When Abram was ninety-nine years old, God appeared to him again." Why did God delay so long? Not simply that we should get to know the just man's endurance and his great virtue, but for us to see as well the extraordinary degree of his power. You see, when nature lost its potency and was now useless for childbearing, his body being wasted and chilled with old age, God put into effect the promise to demonstrate his peculiar power.”

Imported from an open dataset — not yet checked against the printed edition.