One of the common questions I have heard from atheists is whether I would sacrifice my own son if God asked me to do it. In saying this, they are referring to the time that God told Isaac to go up the mountain and build an altar and put Isaac on it. Gen 22:1-2 After these things God tested Abraham and said to him, "Abraham!" And he said, "Here I am." 2 He said, "Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you." The question about the command to sacrifice Isaac is meant to suggest that the God of the Old Testament is a cruel God. Would you do what this "cruel" God commanded if he said the same thing to you? My answer is always the same. "God is not cruel and would not command me to do that and you have completely missed the point of what he commanded Abraham." God has always proclaimed to us that he would provide a substitutionary sacrifice for our sins.
There are a few reasons we can know that Isaac was never in danger.
1. Genesis 22:8 Abraham said, "God will provide for himself the lamb for a burnt offering, my son." So they went both of them together. Abraham already believed in God's provision of a substitutionary sacrifice.
2. Genesis 17:19 God said, "No, but Sarah your wife shall bear you a son, and you shall call his name Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him. Abraham already knew that Isaac was a son of promise, and that God had promised that Isaac would have offspring and that God's covenant would be renewed with him. Abraham believed that God would fulfill this promise as he walked up the mountain with Isaac and wood for the altar.
3. Romans 4:16-17 That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring--not only to the adherent of the law but also to the one who shares the faith of Abraham, who is the father of us all, 17 as it is written, "I have made you the father of many nations"--in the presence of the God in whom he believed, who gives life to the dead and calls into existence the things that do not exist.
The Apostle Paul tells us that Abraham believed that God was a God who brings the dead to life.
When you put all these into place you realize that Abraham believed that God would provide a substitutionary sacrifice, that God's promise of Isaac's future would be forthcoming, and that God can raise the dead to life. He knew that God's character and promises would prevail, and they did.
The test that Abraham was given showed to Abraham and to us that our faith in God's promise of salvation is a faith in God's provision of a substitutionary atonement for sin. While Isaac is insufficient as a son of promise to make sacrifice for our sin, God's substitution points to the fact that he would give his own Son. Abraham's faith in God's substitutionary sacrifice was not faith in an animal on the altar but faith in God who forgives sins and brings death to life. The point of Genesis 22 is that Abraham had the same faith as we do as he looked forward to the fulfillment of God's promise. Abraham anticipated Jesus, we have faith in the Jesus who has already been revealed as the Son of promise and has accomplished his task.
The point of the matter is this. There is one gospel. There always has been one gospel. The good news that God has provided a substitutionary sacrifice to atone for his righteous wrath upon our sin so that through faith in his Son of promise we might be forgiven of sins and go from death to life. The biblical message is that ever since Genesis 3, we have always needed a substitutionary sacrifice for our sin - JESUS.