 A good way of underlining the basic point here is by setting out an alternative formulation of the argument from evil in which it is granted, for the sake of argument, that there is an omnipotent and omniscient person.  The result of doing this is that the conclusion at which one initially arrives is not that there is no omnipotent, omniscient, and morally perfect person, but rather that, although there is an omnipotent and omniscient person, that person is not morally perfect, from which it then follows that that there is no omnipotent, omniscient, and morally perfect person.