The argument is that if God is all-loving, all-powerful, and all-knowing, then the existence of evil is inexplicable, for such a God could create a world without evil—he has the power and the knowledge to do so—and he would create it, for his love would require that he do so. According to the argument, therefore, the existence of God is incompatible with the existence of evil. For many, the suppressed conclusion is that it is irrational to believe in God if one recognizes the existence of evil, as most people do.

By pointing at the non-integratibility of evil, the problem of theodicy shows us that evil is, indeed, a horror. But the problem can reveal that horror only if no solution to it is finally satisfactory. As I said in my criticism of Leibniz, any solution to the problem of evil, any integration of it into a rational theology, amounts to an argument that there is, in fact, no real evil and that stoicism rather than horror ought to be our response to suffering. It follows that if a theodicy solves the problem of evil, then it justifies Satan. Only if the problem of theodicy is genuinely a problem—only if all solutions ultimately fail—can we continue to know that evil is genuinely evil.