The story of Abraham's near-sacrifice of his son on Mount Moriah is one of the formative myths of Western monotheism. And most theists of the Jewish, Christian and Islamic traditions look up to Abraham as a model of faith, believing that his willingness to kill his own child in obedience to God's command is a praiseworthy character trait. But as I wrote in "A Book of Blood":
That the sacrifice was not actually carried out does not change the moral revulsion we should feel at this episode. What kind of god would demand a man prove his obedience by murdering his only son? And more so, what kind of man would obey such a command? Abraham has been held up as an archetype by Judaism, Christianity and Islam alike, but is this really the sort of behavior we should strive to emulate - the willingness to kill in God's name? Had I been in Abraham's place, I would have thrown away that knife and let Jehovah know, in no uncertain terms, that I would never serve any deity who demanded such a price. And had I been in God's place, that is exactly the response I would have rewarded.
But no. The God of the Bible rewarded - blessed, actually - a man who would have slit the throat of his son on command. Evidently, this is the quality Jehovah values - not humanistic morality, not an unshakable respect for human life, but a willingness to lay one's conscience aside and blindly obey.
Going further with this, I have a question for every religious believer, based on the Abraham episode: Do you believe that violence in God's name is wrong, or do you merely believe he hasn't personally told you to do violence? If God appeared to you and spoke to you, commanding you to commit a violent act - to murder a child, say - how would you respond?
If your answer is that you'd never commit an act of unprovoked violence against another human being, no matter who told you to do it, then congratulations! You're a better person than the character of Abraham and possess a more developed moral sense than the author of that story, and you ought to be applauded for that. It's that kind of rational, humanistic morality that's led humanity out of the dark ages of bloodshed and tribal warfare fossilized in the pages of the Bible.
If your answer is that you'd reject that command because you're certain that the god you believe in would never order such a thing, and any such order would have to be a hallucination or a misunderstanding, then you also deserve accolades - though a bit more cautious and tentative in this case. From an atheist's perspective, it's worrying to find someone who abstains from violence not because they recognize the intrinsic badness of violence, but merely because they believe it's not the method God finds most convenient to achieve his goals. Honestly, this answer is a dodge. It ducks the hypothetical posed in the question: If God appeared before you in all his glory, and if he gave you a clear, explicit and unmistakable command to go stone an adulterous woman or strap on a suicide vest - how would you respond? That dilemma is the core of the Abraham test. (You could, of course, say that God recognizes the intrinsic badness of violence, but that would require discarding huge swaths of the Bible.)
If, on the other hand, you would gleefully go out, murder and pillage if God gave you the green light - well, that's an abhorrent and frightening answer, though it's one that's evidently shared by millions of theists in the world today and throughout history. A vast number of atrocities, from genocidal war to honor killing to slavery to child abuse, were and are justified by claiming that it was God's will to commit all of them.
What this belief leads to is a kind of nihilism, where there's no enduring standard of morality other than what God happens to command at any given moment, and he might command absolutely anything. It goes without saying that this belief also makes people willing foot soldiers for the prompting of bloodthirsty demagogues and dictators; once you've trained yourself to put your conscience to sleep, it becomes that much easier next time, especially when the person urging you to do it claims to speak in God's name.
By mindlessly following the model of Abraham, humanity has made its history a chronicle of bloodshed, violence and unending holy war. However, as the world becomes more tolerant and peaceful, there's a countervailing current of humanistic morality that's taken hold to a greater extent than most people realize. I think that most people, even the devoutly religious, would no longer be willing to sanction murder of nonbelievers in the name of God (though there are notable exceptions). I just think that most of these people have never faced up to the contradiction in their own minds. The Abraham test may be a useful way to highlight the chasm between the morality of the Bible and the better, less violent and more humanistic morality espoused by most citizens of the modern world.
Image: "The Sacrifice of Isaac" by Caravaggio, via Wikimedia Commons