This same basic principle is why the first law of time travel seems reasonable to us. What is the first law of time travel? Come on McFly! You don't mess with the past, of course. Some science fiction stories take this to the extreme and suggest that even bending a single blade of grass differently could dramatically alter the future--probably bringing about a premature apocalypse. Yet, to a certain extent, I think we can still imagine how (if time travel were possible) that might make sense. We know that because we have seen how tiny variations can produce huge changes over long periods of time. For instance, if you are building a railroad and you lay down the tracks even slightly off from parallel, the train my be able to run fine for a while, but given enough time, the tracks will eventually move far enough apart, and the train will crash or be ripped apart.
We should all be on the same page thus far. We get it. We know that mosquitoes have an important role to play, even if we don't understand all of the particulars. And we have seen that tiny variations can produce huge changes over long periods of time. However, as soon as we are confronted with the problem of evil, pain, and suffering--at large, or in our own lives--we all seem to flip back into thinking, "Why did that have to happen? Someone give me just one good reason. What would it really hurt if God just zapped that event so that it never happened?" Do we really suppose that it is so simple? Is any event in history so isolated that it has no impact on any other event? Skeptics will insist, "It shouldn't be hard for an omnipotent God." But it really isn't a question of whether or not God could alter or eliminate a particular happening. Of course he could (on the Christian view). The real question is "why doesn't he?" At this point, many skeptics of Christianity will confidently declare victory. "Gotcha! If your God could do something about insert event, but doesn't, that means he is evil. Deal with it," they say. But they can only do that by slipping back into the sort of thinking that I had as a child about mosquitoes; namely, that I know enough about the way our ecosystem works to say that mosquitoes serve no function beyond simply irritating me. Therefore, I concluded (as a child), if God allows mosquitoes to remain in existence, then he obviously wants me to be miserable. Of course, I don't think that now. Why? Because I have information now that I didn't have then. I still don't fully grasp the relationships and functions of every little creature. I am not a biologist, but I know enough to know that there is more to the existence of mosquitoes than, "God is a big jerk." Why then is it so difficult to understand that no one has adequate information to say "God (if he exists) didn't stop insert event, and the only reason for that must be that he is evil"? The only way to make such a judgement would be to have the mind of God. We would have to be able to get out of our place in time and space (hey, that rhymed), view the whole picture, and understand the role of each thread in the fabric of reality. How much can the train tracks be moved before the train of the universe, and human existence comes completely off the rails? We don't have that information. Without that, we are just kids complaining about mosquitoes.
In the same way that a basic understanding of how ecosystems work is all I really need to know in order to conclude that existence of mosquitoes isn't pointless, or proof that God is mean, I can get a basic understanding of God's nature from what is revealed in Scripture, and that is all I really need to know in order to conclude that the (temporary) existence of pain, suffering, and death is not meaningless, or proof that God is evil. What is the biggest indicator? The death and resurrection of Jesus Christ. God became a man, experienced pain, rejection, suffering, betrayal, and even death--he entered right into the middle of the worst of it all. That would be enough to let us know he isn't distant and uncaring. But it would not necessarily give us hope. The good news is that Jesus overcame death, left behind an empty tomb, and now offers life to all who will put their trust in his finished work.