If Abraham had gone ahead and killed his son he would have done something morally wrong. A father has a basic duty to look after his son, and certainly shouldn't tie him to an altar and cut his throat in a religious ritual. What God asked Abraham to do was to ignore morality and make a leap of faith. In the Bible Abraham is presented as admirable for ignoring this normal sense of right and wrong and being ready to sacrifice Isaac. But couldn't he have made a terrible mistake? What if the message wasn't really from God? Perhaps it was a hallucination; perhaps Abraham was insane and hearing voices. How could he know for sure? If he had known in advance that God wouldn't follow through on his command, it would have been easy for Abraham. But as he raised that knife ready to shed his son's blood, he really believed that he was going to kill him. That, as the Bible describes the scene, is the point. His faith is so impressive because he put his trust in God rather than in conventional ethical considerations. It wouldn't have been faith otherwise. Faith involves risk. But it is also irrational: not based on reason. Kierkegaard