The question of the origin of evil has challenged thinkers and theologians back to earliest times. The question, "Why do bad things happen to good people?" is the theme of the oldest book in the Bible, Job. In Christian theology, the subject has such a long history that it has its own name, "theodicy" -- which generally means the attempt to justify the ways of God in light of the existence of evil. Here, evil may be construed as either "natural evil" such as diseases, violent weather, earthquakes and the like, or "moral evil" involving the infliction of injustice, cruelty etc. by people.
In modern times, Antony Flew, the 20th-century skeptic, reduced the question of moral evil to simple terms. First he quoted the objection derived from Thomas Aquinas:
"It seems that God does not exist. For if of two contrary things one were to exist without limit the other would be totally eliminated. But what is meant by this word 'God' is something good without limit. So if God were to have existed no evil would have been encountered. But evil is encountered in the world. Therefore, God does not exist."
Flew elaborates this objection as follows:
"The incoherence -- or perhaps on this occasion I should say only the ostensible incoherence -- is between the idea of creation, as necessarily involving complete, continual and absolute dependence of creature upon Creator, and the idea that creatures may nevertheless be sufficiently autonomous for their faults not to be also and indeed primarily His fault. The former idea, the idea of creation, is so essential that it provides the traditional criterion for distinguishing theism from deism. The latter is no less central to the three great theist systems of Judaism, Christianity, and Islam, since all three equally insist that creatures of the immaculate Creator are corrupted by sin. So where Aquinas put as his first Objection a statement of the traditional Problem of Evil, conceived as a problem of squaring the God hypothesis with certain undisputed facts, a redactor fully seized of the presumption of atheism as expounded in the present paper would refer instead to the ostensible incoherence, within the system itself, between the concept of creation by a flawless Creator and the notion of His creatures flawed by their sins."
How should we understand the origin of evil and the answer to this objection?
If one is a believer in a good God, then one must face Flew's objection that this belief lacks coherence. Theologians have long confessed that they do not have a completely satisfactory response to this objection. However, we do have an explanation for why they do not have such a response.
First of all, it is important to note that the theodicy question is uniquely problematic, because no one stands in a neutral position. Everyone has a vested interest, one way or the other, in the alternative answers. From an atheistic point of view, the "God" of the Bible has some arbitrary reasons for objecting to certain behaviors of people who simply want to do as they please.
From the Biblical point of view, we are all sinners, and one of the consequences of sin is that our minds are blinded to the origin of evil. As sinners, we live our entire lives in a sinful world. As a fish "does not know what water is" because of a lack of contrasting elements, so we lack any experience of a sinless world, or a sinless mind, with which to see clearly through the fog and darkness of our own corruption (what theologians call the "noetic effects of sin"). And this is not only a condition of ignorance, but wilful ignorance, because sinners don't like anyone to judge their behavior. From this Biblical viewpoint, we can interpret atheism as merely a defense mechanism for sinful behavior and to evade moral guilt, by denying the existence of a righteous, judging God.
Christians have an even more profound answer to the question of evil, which includes both natural evil and moral evil. As Catholic theologian Jack Haught explained it [in 101 Questions on God and Evolution]:
"... according to the Christian faith, the passion and resurrection of Jesus present us with the portrait of a God who shares fully in the suffering of this world and who rises victoriously over it. There is no easy theoretical solution to the problem of suffering, but we may hope for an eschatological one: God will "wipe every tear from their eyes, and there shall be no more death and mourning, wailing or pain ..." (Rev. 21:4). We can assume that this final consolation applies to the whole of the life story and not just to the human episodes.
"The struggle and pain in evolution are certainly not contrary to a Christian interpretation of the world in terms of the cross of Christ. Christian experience, moreover, implies that suffering can have a transformative quality. If we are attuned by faith to the conviction that suffering can lead to something higher, then we will not be completely taken aback by the Darwinian picture of natural history. And if we frame the whole of nature within the scheme of hope and promise of resurrection, Christian faith allows evolution process to be redemptive as well."
So Christian theologians don't have a complete answer to the question of the origin of evil, but they do have a meaningful explanation for why we don't have such an answer, and this explanation is coherent with the rest of Christian theology.
Hence the trilogic illustrations on this topic are not really an attempt to pinpoint the nature of evil or its origin, but rather how the existence of a good God and the reality of evil are not incoherent or mutually exclusive ideas in Christian theology.
This topic is closely related to the trilogic on Nature, where the mysterious nature of change in creation is explored. This includes a further treatment of "natural evil", which embraces destructive events or "Acts of God" that have no moral component.