Gen 17:27

“Consider, on the other hand, I ask you, dearly beloved, God's loving kindness and his unspeakable kindness to us. In that case pain and distress resulted from the action and no benefit came from circumcision, except simply making people recognizable through this sign and separating them from the other peoples. Our circumcision, on the contrary—I mean the grace of baptism—involves a painless medicine and is the means of countless good things for us, filling us with the grace of the Spirit. It has no limited span as in that other case, but rather in early years, in middle age and in the very height of old age can a person receive this circumcision—not the work of human hands—which involves not simply endurance but laying aside sin's burden and finding pardon for the faults of all time.… The loving God saw the extraordinary degree of our limitations and the fact that we are suffering from incurable diseases and need a lot of care as well as his ineffable love. [Thus] he is in his provision for our salvation granted us the renewal that comes from the bath of rebirth, so that by setting aside the former person—that is, evil deeds—and putting on the new we may advance along the way of virtue.”

“And all the men of his house,.... All the males, whether children or adult: born in the house, or bought with money of the stranger, were circumcised with him; by their will, and with their consent; not forced to it, as Aben Ezra rightly observes; and these being before trained up by him in religious exercises, were more easily prevailed upon by him to follow his example; this also is repeated, that it might be served, and be an example to follow in after generations. Next: Genesis Chapter 18”

“Learn fully then, children of love, concerning all things, for Abraham, who first circumcised, did so looking forward in the spirit to Jesus and had received the doctrines of the three letters. For it says, "Abraham circumcised from his household eighteen men and three hundred." What then was the knowledge that was given to him? Notice that he first mentions the eighteen, and after a pause the three hundred. The eighteen is I (= 10) and H (= 8)—you have Jesus—and because the cross was destined to have grace in the T he says "and three hundred." So he indicates Jesus in the two letters and the cross in the other. He knows this who placed the gift of his teaching in our hearts.”