98 The father offered indeed his son, but God is appeased not by blood but by dutiful obedience. He showed the ram in the thicket in the stead of the lad, that He might restore the son to his father, and yet the victim not fail the priest. And so Abraham was not stained with his son's blood, nor was God deprived of the sacrifice. The prophet spoke, and neither yielded to boastfulness nor continued obstinate, but took the ram in exchange for the lad. And by this is shown the more how piously he offered him whom he now so gladly received back. And thou, if you offer your gift to God, dost not lose it. But we are tenacious of our own; God gave His only Son for us, we refuse ours. Abraham saw this and recognized the mystery, that salvation should be to us from the Tree, nor did it escape his notice that in one and the same sacrifice it was One that seemed to be offered, Another which could be slain.
Source: On the Death of Satyrus (New Advent)