The existence of evil is quite possibly the most troublesome fact to reconcile with our faith. Everything about Christianity stresses over and over, that God is good, Good, GOOD. Yet it's only natural, then, to wonder why such a "good" God allows evil in the world. Why do innocent children get sick and die? Why do tsunamis devastate the lives of thousands of people? The list goes on...
There are a couple of precursor points I'd like to make. First, there's a time and a place to discuss this topic. In the moment of grief, when someone is crying out in pain, "WHY???" --- that is generally NOT the time to launch into a philosophical or theological diatribe, as it's really a request for compassion, not a long-winded answer. Philosophy can wait for a less emotional time. The second point is that, at some point and time, every single one of us will be that emotional person. And the time to be prepared for it is NOW, when we are able to think calmly about it. The less prepared for it we are the more likely such moments of grief will become serious challenges to our faith.
Of course, the only final, difinitive answer to the question of evil is to look at the cross. We can say that Jesus Christ became evil for our sake. By this we don't mean that he was actually evil, but that he took upon himself the consequences of evil. There is, at our disposal, a lifetime's worth of reflection on this fact, and we will still only have skimmed the surface.
But there is another way of approaching the subject, too. One of our assignments for our Fundamental Theology final exam, in fact, was to explain how one can circumvent the problem of evil philosophically (recall that philosophy = "natural" theology), without relying on God's revelation to man (in other words, without talking about Christ). As deep as the mystery of Christ's suffering is, we only know about it because it was revealed to us through Scripture and Tradition. Someone who doesn't accept Scripture and Tradition will not find a reflection upon Christ to be a useful way of resolving the problem of the existence of evil in the world, and in fact will find evil to be a barrier to ever accepting the Christian notion of a "good" God or even of the existence of a God at all. Their argument will likely go:
If God is all-good and all-powerful, then He would not will evil, and would have the power to make sure it doesn't happen. Since evil exists, either God is not good or He is not all-powerful.It's a conundrum for the Christian to answer, because we do believe that God does not will evil, and we also believe that He is all-powerful. But we don't accept that the above conclusion follows from the premises given. The tricky part, then, is in countering this argument without resorting to the negation of God’s attributes of “good” and “all-powerful.”
This is how you do it: The first integral step is to ensure a correct definition of evil. The common misperception about evil is that it is some thing; it has an existence, or being, of its own, which is opposed to goodness. Yet this dualistic understanding of good and evil ascribes evil more credit than is its due, for the correct definition is that it is rather an absence of something good, a privation. Existence, in and of itself, is a good bestowed by God. Evil rears its ugly head when some aspect of existence that is due a thing by its very nature is not present. That is, evil is encountered when something ought to possess some good, but does not. If I, as a human, am supposed to have two arms, but I only have one, then I am experiencing an evil. As a contrast, I do not experience evil by not having a tail, for humans are, by nature, not supposed to have tails.
A second step in overcoming this argument is by making clear the distinction and connection between the types of evil: moral evil and physical evil. As embodied creatures, humans generally experience what we consider physical evil (disease, injury, etc.) most vividly. Yet moral evil is no less present in human experience, if perhaps more subtle. As moral agents with free will, men are always capable of sinning, by making lesser choices that do not allow them to attain some good which they rightfully should possess. This deficiency is a moral evil. With this distinction in place, there is a correlation between physical and moral evil that provides the explanation for how they came to be. The greatest moral good that a person can possess is God himself; a right relationship with the Creator. Yet the common condition of all humans is that we do not possess this good; rather our relationship with God begins, from our very birth, broken. Among the effects of this deprivation include the exposure to physical evil in the world. Moral evil is therefore, properly speaking, the preeminent evil, and all evil can be explained by the presence of the broken relationship with God (i.e. Original Sin).
One further thing must yet be demonstrated to see that God can be good, all-powerful, and still allow evil in the world. God’s tolerance towards moral evil can be shown to be a result of His protection of a greater good. Human beings are free moral agents; free will is a good that is due to men by their nature. It is true that man experiences moral evil because of the poor choices of his free will. Yet if God were to remove free will, then that would be another absence of a good due to man by his nature, and that by definition would be a moral evil. God, of course, is good and cannot will evil. Therefore, by tolerating the evil brought about by man’s free will, God is protecting the greater good of keeping man free to choose his own actions.
So there you have it. In a nutshell, evil is the result of man's free will, and therefore God allows evil to continue in the world because it would be evil for Him to remove our free will.
Of course, this argument only brings you so far. If you believe that Christ died for our sins, then you will find an inexhaustible amount of reflection on the problem of evil by meditating on this: