Most of the monotheistic religions regard some degree of suffering as the route to perfection or, at least, to self-improvement. Suffering is often connected to the spiritual advancement through hardship, the mortification of the flesh, penance, compassion, the notion of destiny (salvation and damnation) and ultimately, the reign of good over evil.
In Christianity, the concept of suffering is related to the life, and death, of Jesus. As Jesus suffered on the cross to save humanity, so his followers have to suffer through their lives to attain life after death. Christians are often troubled by the dilemmas of good people suffering, for instance when innocent children fall ill and die. The notion of theodicy, coined by philosopher Gottfried Leibnitz (1646-1716), seeks to explain this. Free will theodicy states that albeit being good, God is also a creator of free creatures and therefore cannot determine everything that they do. If a creature is able to exercise free will to do good, then it must also have the option to choose evil, too. Suffering exists because some of God's creatures have chosen evil over good and are justly punished for their actions.
Free will theodicy may justify moral evil but it does not explain the existence of natural evil, such as earthquakes or floods. One theory attributes these misfortunes to demonic beings, such as Satan or fallen angels, while others claim that they are a punishment for original sin. A possible explanation is also given by the educative theodicy, which states that any evil serves as a stimulus for enhancing moral character, gaining experience and developing human strength.
Similarly, Judaism also deals with the contradiction between a benevolent and omnipotent God and the existence of suffering. If God is merciful and loving, then it is apparently contradictory that he does not spare his children the pain. Theodicy is rooted in the Hebrew Scriptures. The Bible (in Genesis) sees the good world, created by God, as corrupted by human sins. It blames suffering entirely on human inability to exercise their free will to create good and resist temptation and sin. Kabbalah, the Jewish mystical school of thought, justifies suffering as a means of discriminating between God and the people and constitutes the pain of separation from God.
Turning to Buddhism, The Four Noble Truths, which contains the most important principles of the religion, explain that dukkha (suffering) can be defined as: "birth is dukkha, old age is dukkha, disease is dukkha, dying is dukkha, association with what is not dear is dukkha, separation from what is dear is dukkha, not getting that which is wished for is dukkha…" A central question in Buddhism is why does pain and suffering exist?
Hinduism links suffering to the notion of karma (deed, or act). According to karma theory, every action has its consequences, either in this life or in a next reincarnation. In contrast to the believers in destiny, Hinduism gives its followers the free will to decide on their actions but inevitably accept the effects from them. Through karma, good actions bring positive results and bad actions cause suffering. The effects may not appear instantaneously, though. Accumulation of good karma over several lifetimes may lead to a next life full of well-being, joy and serenity. Karma may influence the life form in which the soul reincarnates - accumulation of bad karma may mean that a soul will live in the body of a lower form of being.
Suffering in Islam is also a way to cleanse the soul and to rid the self of sins. It is viewed in ways very similar to Christianity and Judaism. The difference there is that Islam does not question or doubt God's decision to send suffering to his believers. It is either sent by him as a test or as a punishment for a sin. Followers are taught never to resist suffering but to live through it with faith and hope, believing that god never gives you more than you can endure. Islam clearly states that suffering must not be self inflicted or inflicted upon others; it is only God who can decide when someone should suffer.