Athanasius of Alexandria

Here is a man of true faith, for when the Lord asked him to sacrifice Isaac, his only son, he was willing to do so. By faith he offered up the one through whom the Lord had given him the promise of a nation of descendants. And in offering his son he worshiped the Son of God. When the Lord held him back from sacrificing Isaac, Abraham saw the Messiah in the ram that was ultimately offered as the sacrifice to God.We see, then, that the patriarch was tested by means of Isaac—not that Isaac was sacrificed but rather the one who was pointed out in Isaiah, "He shall be like a lamb that is led to the slaughter, and like a sheep that before its shearers is dumb." He was, in truth, tested by him who took away the sin of the world.
That is why Abraham was held back from laying his hand on the boy. If he had sacrificed Isaac, the Jews might very well have rejected all the prophecies concerning the Savior. Undoubtedly they would have especially rejected such prophecies given by the psalmist as, "You have not wanted sacrifice and offering; for you have prepared a body for me." They would have referred all such prophecies to the son of Abraham.
Thus the sacrifice was not for the sake of Isaac but of Abraham, who was tested by being called upon to make this offering. And of course, God accepted his intentions, but God prevented him from slaying Isaac. The death of Isaac would not buy freedom for the world. No, that could be accomplished only by the death of our Savior, by whose stripes we are all healed. He alone picked up the falling, healed the sick, satisfied those who were hungry and filled the poor. Above all else, he alone raised us all from the dead, and having abolished death, he has brought us from sorrow and sighing to the rest and gladness of this feast. That, dear friends, is a joy that reaches heaven!