Like all monotheists (those who believe in one God), Protestants confront a dilemma on the subject of evil and suffering. Does God want to relieve suffering, but is unable? In that case God is good but not all-powerful. Is God able to relieve suffering but unwilling or too unconcerned? Then God is all-powerful but not good.
Protestants agree that the universe was created from nothing by God, and it was created good. This is the doctrine of creation ex nihilo. God is omnipotent and, prior to the effects of evil, Creator of all that is. There is no property of matter that in and of itself could account for evil—creation was good. Therefore evil and suffering entered the world through something other than God's original acts of creation. God is not the creator of evil. (For many modern Protestants this belief is not incompatible with evolution; God created the universe in such a way that creation unfolds through the mechanism of evolution.)
The entrance point for evil and moral suffering in the world, then, is the fall and work of Satan, and human rebellion against God (that is, sin). Protestants do not always agree on why sin entered the world. Those who believe that the story of the fall recounts a historical event agree that Adam was tempted by the devil. But why did Adam, created without sin, succumb to temptation? One set believes that Adam could have chosen not to sin. In order to create a genuinely free being with whom God could enter into a relationship, God gave Adam free will. Adam made a bad choice. This belief dovetails with a belief that salvation in part requires the individual's free choice to ask for forgiveness and for help in following God's law.
Other Protestants argue that this places too much control over the course of history into the hands of humans rather than God. They argue that Adam sinned necessarily, though not by compulsion; this makes God at least indirectly the author of sin. This second group splits on why creation was set up this way. Some believe that God's mercy and glory are more fully demonstrated in a world in which sin enters, and is then forgiven and defeated. Others believe that scripture simply does not answer this question, that God's ways are not human, and that it is not the place of human beings to interrogate God on why sin entered the world. Zwingli and Calvin belong here. They agree that sin is an act of human disobedience against God's command, and that this disobedience is entirely humans' responsibility.
For Calvin, since the time of the fall (Adam's original sin), one cannot say that humans sin by compulsion, because that would indirectly make God the author of sin. But one can say that humans sin inevitably. When they sin, they are doing what they want to do. But on the question of human responsibility for sin and the role played by God, this claim of human responsibility simply pushes the problem back to square one. Could not God have created humans in such a way that they would not sin? In the end Calvin, and many other Christians with him, says that humans are not privy to God's plans, and that it is inappropriate to question them or speculate about them.
While these theological moves seem to delay assigning responsibility to God for sin, in the end many people think that Calvin cannot avoid this claim. This is a root of the Arminian controversy, and it is this dispute that, perhaps more than any other, separates Reformed Christians from Methodists and other Arminian (or Arminian-like) traditions. In the end, while continuing to assert that sin is a human responsibility, Calvin's strong emphasis on God's omnipotence means that the answer to the question of why God allowed sin to occur, or why God set up the universe in such a way that it could occur, is simply a mystery. Methodists have a foot in both camps here, wanting both to emphasize God's omnipotence with the Calvinists, and to maintain a degree of free will in choosing to accept God's grace.
Though sin in the world is the source of human-caused suffering—evidenced in war, violence, poverty, hatred, anger, etc.—some of the suffering is perceived to be a direct outcome of individual and social behavior and thus a natural consequence, and some of it is perceived to be divine punishment. There is much diversity of belief around the meaning of suffering.
Most Protestants differentiate between suffering caused by sin and evil, as discussed above, and physical or natural suffering—evidenced in earthquakes, tsunamis, tornados, etc. While all suffering enters the created order because of the original break in relationship with God, not all suffering today has a moral source. That is, the natural order of creation is also broken, and thus tragic events occur in the world that display that brokenness but are not directly caused by some moral breach. Not all suffering is caused by sin. God sometimes permits suffering, even though God could have prevented it, for purposes that are beyond human understanding. The story of Job is a good example of this.