Why is there evil and suffering?

Answer 1

In God’s original Creation there was no evil. No suffering. But when Adam and Eve sinned, suffering and evil and death was brought into the world. But what was the cause of the sin? The answer is free will. God could have created mankind as robots who did exactly what God said. But instead God gave us free will. He gave us a choice to obey or rebel. And when man chose and chooses to rebel, the consequences are evil, suffering, and death in the world.

Answer 2

There's a lot that can be said here, but I could briefly summarize some answers that theists have suggested (assuming that you're asking about the problem of evil in a world a God created). Each of these is commonly referred to as a theodicy: a way of vindicating an omnipotent, omnibenevolent, and omniscient God in light of there being evil in the world. A common theme is that these theodicies suggest that there is some greater good that God could achieve only by allowing evil in the world. Here are some well-known ones (along with objections):

1. Retribution: God allows (or causes) suffering in the world, but this suffering is not evil since it is only just punishment for humanity's sin or disobedience. (Obj: Doesn't explain why God allows humanity to sin, which is a source of evil)
2. Free Will: The ability to choose to do good or evil is something that God would want us to have, and he finds it worth giving it to us even if it does result in there being evil in the world (Obj: What about natural evils, like hurricanes or earthquakes?)
3. Soul-Making: God allows evil in the world because it is the only way to provide humans the opportunity to genuinely develop their moral character. (Obj: There seem to be evils that don't seem to benefit us in this regard at all)
4. Some Combination of the Above: Adopt a theodicy that suggests that some evils/suffering could be allowed for different reasons, such that some are required for retribution, others for free will, and the rest for soul-making. (Obj: Consider the Holocaust or some other horrific evil. Did the victims in a genocide really deserve that? Couldn't there be free will without there being genocide or some equally horrific evil? Why not use less horrific evils to develop the moral characters of those involved?)
5. Skeptical Theism: For at least some evils that God allows, we ought to believe that He has some reason for allowing it, but we should be skeptical of our own ability to know or understand what those reasons are. Appeals to parent-child analogies are common here, as for example, a parent allows the child to endure pain from going to the dentist even if the child can't understand the benefits of going to the dentist. (Obj: Analogy is problematic. A parent might not have a choice about whether or not the child could understand the reasons for allowing some evil/suffering, but certainly God has the power to create us such that we'd be able to understand why he allows evil)