The problem of Evil is a classic theological and philosophical problem. Put briefly, the problems arises because of the difficulty of reconciling God’s qualities with the existence of evil in the world. Despite numerous new books on the subject, the problem of evil is rather old. In fact, the fundamental philosophical problem dates back to Plato.
The simplest and most concise form of the problem of evil can be nicely presented as a deductively valid argument:
Premise 1: If God exists then there would be no evil.
Premises 2: There is evil.
Conclusion: God does not exist.
A more complex version of this argument is based on the assumption that God is all good, all powerful and all knowing. If God is all good, then He would neither tolerate nor permit evil. If God is all powerful, then God can prevent all evil. If God is all knowing, then no evil can be hidden from God. So, if God is all good, all powerful and all knowing, then there would be no evil. Since there is evil in the world, it follows that either God does not exist or God lacks at least one of those attributes.
An interesting variation on this problem can be used to counter the classic argument from design. The argument from design (presented in its simplest form) works like this:
Premise 1: There can be no design without a designer.
Premise 2: Life, the universe and everything clearly show signs of design.
Premise 3: The only entity capable of designing the universe is God.
Conclusion: Therefore God exists.
The idea behind this reasoning is that we can infer the existence of God by observing empirical facts about the universe. However, if this method is accepted, then it leads to the variation of the problem of evil. If the apparent design of the universe leads to the conclusion that God exists, then the presence of evil and imperfection would seem to entail that God, if He exists at all, is evil, sloppy or otherwise deficient. Naturally this conclusion does not fit well with the conception of a perfect being.
Most of the plausible replies to the problem of evil involve trying to reconcile the empirical facts (evil and imperfection) with the theological assumption of God’s perfection. While none of these arguments are conclusive, they do provide a rational basis for accepting God’s existence in the face of the problem of evil.
In my own perspective, the problem of evil is perhaps the greatest barrier to belief in a perfect God-at least for those who follow reason. While one often suggested option is to abandon reason and simply go on faith, that option is rather problematic. After all, giving up reason as a means of assessing theological claims leaves one rather defenseless against all sorts of foolishness and trickery.
Another classic option is to simply state that God has a mysterious plan and everything will work out in the end. There are two obvious problems with this line. First, if God has a mysterious plan that we do not understand, then how do we know that God is actually good? If the answer is faith, then we are back to the problem raised above. If there is evidence, then it is not a mystery after all. Second, if everything will work out in the end, why not now? I expect imperfect beings to have to work things out, but God should not require time to get things right.
There are many other replies as well, but none seem to provide a full and satisfying reply.