Moral evil and natural evil exists because there is sin in humanity.
Sin originated in the Garden of Eden with the fall of man. Adam and Eve were the first humans, created "in the image of God" (Genesis 1:27 NIV) to tend to the Garden of Eden. Adam and Eve were allowed freedom to eat from any tree in the garden, except they were not to eat from the tree of the knowledge of good and evil. Satan tempted Eve to take of the tree and both she and her husband ate of the fruit. Through this failure to obey God, sin entered the world, and it was not just them who received God's judgment. God passed judgment on the whole creation, not just
man.
While sin explains the existence of evil, theodicy attempts to resolve the problem of evil by showing God is omnipotent and all-loving even though there is evil. Gottfried Leibniz has a view of theodicy that states God does everything for a reason, and His reasons are discernable to us through pure reason. Leibniz says that God would create the best possible world, which by metaphysical definition, must contain both good and evil. The fault in this theodicy lies with the assertion that God would create evil. Other theodicies lean on modified rationalistic theology. These theodicies are the Augustinian tradition of theodicy and soul-building theodicy. The former explains the evil in this world as a result of sin. The sin in the world is a result of the abuse of free will. The soul-building theodicy suggests that God did not intend to create something perfect when He created man. According to the theodicy, a man was to gain moral development while on earth. This development would only be possible in a world with evil. The problem however with this theodicy is that God initially created Adam and Eve in the Garden of Eden, an idyllic environment. Evil began when they first disobeyed God (Feinberg 1185 - 1186).
One of the requirements of a theodicy is that it must be internally consistent. By definition, theodicies are given in response to a logical theological problem. Therefore, it is necessary for the explanation of the logical problem to be itself logically consistent. Furthermore, the theodocist needs only to be logically consistent with his or her theology, regardless of the stand of a critic (Feinberg 1185 - 1186).
Even with belief in a theodicy, a personal experience of evil may affect an individual's relationship with God. A death in a family could lead people away from a relationship with God. Especially, if that death occurred from lung cancer, but the individual who contracted the disease never participated in the typical activities linked to the cause of lung cancer. Through bad advice given to him by his friends, Job had questioned God when he had gone through unexplainable trials. His friends blamed Job's trouble on his sins. Job could have ended his relationship with God as well, but chose differently. If a person disputes a particular belief about God, it doesn’t mean the individual is attacking God. There are numerous theodicies concerning God, challenging one view is not an attack, but a difference in understanding.
While other theodicies exist to conclude how it is possible for an omnipotent, all-loving God to exist with evil in the world, humanities abuse of its free will is the most logical. The evil in the world can come from moral and natural sources.