As a Christian, it can be difficult to reconcile all the evil that happens in the world with an all knowing, all powerful loving God who could stop it if He wants, but chooses not to do so. If our hearts break for the innocent children who were senselessly murdered at Sandy Hook Elementary, how can a God who loves us not feel the same way? If any of us had known what Adam Lanza was going to do, we would have done anything in our power to stop him, so why didn't God? All too often we tend to quote some arcane scripture, chalk it up to God "moving in mysterious ways" and shrug our shoulders. While none of us have the authority to speak for God, there are plausible explanations for why God would choose not to intervene to prevent a tragedy.
1) He gives us free will: God didn't make robots who were designed to execute His will. Instead He gave us the freedom to make our own decisions. He lets us choose between being right and wrong, good and evil or wise and foolish. We can follow Him or scorn Him. We can obey Him or ignore Him. We can take His advice or go our own way. It's our choice...and sometimes choices have terrible consequences. But, of course, how could it be otherwise and still be a choice?
2) It's a necessity for faith: "If God wanted to remove all doubt about his existence, He could do so — but, He doesn’t because the cornerstone of Christianity is faith. Imagine what would happen if bad things DIDN’T happen to good people. What if when an airline crashes, only the non-Christians die while all the believers walk away unscathed? What if the moment someone becomes an atheist, he is immediately struck by lightning and killed? What if every rape, murder, robbery, and painful illness only happens to non-believers? If that were the case, then no faith would be required to be a Christian."