1 After these things God tested Abraham and said to him, "Abraham!" And he said, "Here am I."
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."
After the birth of his promised son, Isaac, Abraham is tested by God. God commands Abraham to sacrifice Isaac - to kill him as an offering to God. This may sound very strange and cruel, since Isaac is supposed to be the fulfilment of God's promises which seem to have finally arrived for Abraham. There are several much larger things going on though.
One important aspect to remember is that Abraham knows God can perform miracles. If God has said that Isaac is the son who will fulfil his promise to Abraham, then Abraham would be proceeding on faith that God would raise Isaac back to life from the dead.
A second important thing to note is that God will not ask anyone today to do such a thing as this. God had a specific purpose in mind here. This episode is another symbolic prophecy of Jesus' coming. The Son of God is to be sacrificed instead of the son of Abraham. As we will see, God doesn't actually intend the death of Isaac.