And they came to the place which God had told them of; and Abraham built an altar there, and laid the wood in order, and bound Isaac his son, and laid him on the altar upon the wood. And Abraham stretched forth his hand, and took the knife to slay his son. And the angel of the LORD called unto him out of heaven, and said, Abraham, Abraham: and he said, Here am I. And he said, Lay not thine hand upon the lad, neither do thou any thing unto him: for now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from me…. And the angel of the LORD called unto Abraham out of heaven the second time, and said, By myself have I sworn, saith the LORD, for because thou hast done this thing, and hast not withheld thy son, thine only son. (Genesis 22:9-12,15,16)
I have a question to ask: Did Abraham do it? No, he did not offer his son, but God says to him, "Because you have done this thing…." You see, Abraham believed God, and he went far enough to let you and me know — God already knew — and to let the created universe know that he was willing to give his son. And so God counted it to him that he had done it. Abraham is justified by faith, but he is also justified before men by his works. He demonstrated that he had that faith.
And "hast not withheld thy son, thine only son." Notice how God plays upon that — because He gave His only Son.
Through this incident, God is making it clear that there will have to be a Man to stand in the gap, there will have to be a Man capable of becoming the Savior of the race if anyone is to be saved. That is a great lesson given to us in this chapter. Abraham said that God would provide Himself a Lamb, and they found a ram and offered it. But God did provide a Lamb nineteen hundred years later in Christ. God stayed Abraham's hand and did not let him go through with the sacrifice of Isaac because it would have been wrong. God spared Abraham's son, but God did not spare His own Son but gave Him up freely for us all.
—From Edited Messages on Genesis by J. Vernon McGee