By silently complying with God's instructions to kill Isaac, Abraham was putting pressure on God to act in a moral way to preserve life. More evidence that Abraham thought that he would not actually sacrifice Isaac comes from Genesis 22:5, where Abraham said to his servants, "You stay here with the ass. The boy and I will go up there; we will worship and we will return to you." By saying we (as opposed to I), he meant that both he and Isaac would return. Thus, he did not believe that Isaac would be sacrificed in the end.
Site by Artimin