In this trilogy of articles I highlighted the key features of an appropriate Christian response to the shooting in Christchurch. My first article focused on the victims; my second article focused on the perpetrator; and my third and final article focuses on the problem of evil. Overall my concern has been to show that Christianity provides a map to understanding and preventing human evil and is also able to meet the philosophical challenge presented by its occurrence.
1. The Problem of Evil
The Problem of Evil is one of the oldest and most notorious objections to the existence of God. Its proponent claims that if God exists we should not experience any evil in the world—for if God is all-good, He would want to prevent evil; and if He is all-powerful, He would be able to do so.  The fact that evil obviously does exist proves that there is no God. In the aftermath of a tragedy like the shooting in Christchurch, even those with a strong belief in God may feel the force of this argument.
2. The Higher-Order Goods Solution
The most persuasive response to the Problem of Evil begins by exposing and rejecting its hidden assumption: That human beings are God’s pets and the universe a playground created for their unmitigated comfort and pleasure—a surmise which a single toothache suffices to falsify. Pleasure and comfort, to be clear, are good. And our world contains a generous quantity of both. But a world that contained nothing but pleasure and comfort would of necessity lack something of immeasurably greater value: What philosophers call “Higher Order Goods.”
Love, virtue, compassion, forgiveness, patience, courage, heroism and moral self-determination are among the Higher Order Goods that would be unattainable if the possibility of moral evil were removed. For, as I have argued elsewhere, all these goods are attained through the exercise of free will; and God cannot create agents with free will and prevent them from doing evil.  It follows that any world of free agents in which the Higher Order Goods are attainable is a world in which moral evil is a distinct possibility. 
In responding to the Problem of Evil a theist need not deny that the creation of a world in which humans experience unmitigated pleasure and comfort would be a morally good act. But he suggests that a divine mind may view the creation of a world like ours as a morally better act. It is good to be a contented animal free of suffering and devoid of moral significance; but it is better to be a saint. And God, being perfectly good, gives to the crown of his creation the very best He has to give: He gives us the opportunity to become saints.
The response gains additional force when we remember that suffering is a temporary feature of the created order and the goods it makes possible will endure forever. Those who develop moral and spiritual virtue during this brief period of suffering and probation will be fit for eternal communion with God at the end of time. We do not view the pain of childbirth as a senseless misfortune—it leads to the life-long bliss of motherly love. And nor should the suffering of human beings be viewed as a senseless misfortune if it leads to the eternal bliss of divine love.
3. The Argument from Particular Horrendous Evils
A skeptic who grants the general form of this argument need not completely abandon his objection. He can recognise that the Higher Order Goods are greater than pleasure. He can accept that any world in which these goods are obtainable is one in which suffering will be an unavoidable possibility. But he can nevertheless object that there is too much suffering. In its most formidable formulation, this objection confronts us with a particular horrendous evil. The American metaphysician Peter van Inwagen offers the following example. Unfortunately, this is something that really happened:
A man came upon a young woman in an isolated place. He overpowered her, chopped off her arms at the elbows with an axe, raped her, and left her to die. Somehow she managed to drag herself on the stumps of her arms to the side of a road where she was discovered. She lived, but she experienced indescribable suffering, and although she is alive, she must live the rest of her life without arms and with the memory of what had been done to her.
Inwagen calls this attack “The Mutilation” and asks: Are God’s ultimate purposes dependent on the occurrence of The Mutilation? It would seem not. Then could God have prevented The Mutilation and still achieved his ultimate purposes? It would seem so. It follows, the skeptic continues, that the Mutilation is unnecessary. And since God is all-good, He will want to prevent unnecessary horrors; and since God is all-powerful, He will be able to do so. The Mutilation proves that God does not exist.
4. The Impossibility of a Non-arbitrary Limit
Inwagen, himself a theist, responds to this objection by noting that there are situations in which the imposition of a non-arbitrary limit is logically impossible. And God seems to be in this situation with respect to the number of evils He allows.
After all, subtracting The Mutilation from history does not de-fang the objection from Particular Horrendous Evils. The skeptic could just point to another evil—perhaps the shooting in Christchurch—and ask all the same questions. But nor is a proponent of the Objection from Particular Horrendous Evils denying that the occurrence of some horrors is consistent with the existence of God. The specific assumption underlying the objection is therefore as follows: There is some minimum number of horrors n consistent with God’s plan such that the addition of a single horror (n+1) will represent unnecessary suffering that God, if He existed, would prevent.
In his article on the subject  Inwagen shows that this assumption is false. For any n, where the existence of n horrors is consistent with God’s plan, n-1 will be equally consistent. To ask What is the minimum number of horrors consistent with God’s plan? is therefore like asking, What is the minimum number of raindrops that could have fallen on England that is consistent with England’s having been a fertile country? Obviously, if God had stopped one or one hundred or one million raindrops from falling, England would still be a fertile country. And just as obviously, if God had allowed only one or one hundred or one million raindrops to fall, England would be an arid country. The point is this: It cannot be coherently postulated that there is some minimum number of raindrops n such that the subtraction of one raindrop (n-1) results in England being arid and the addition of one raindrop (n+1) wastefully exceeds what is required to ensure that England is fertile. But that is more or less what the Argument from Particular Horrendous Evils does postulate.
Evil is an emotional subject and Inwagen’s talk of arbitrariness may make some uneasy. It needs to be emphasised strongly, therefore, that while there is no non-arbitrary limit to the quantity of evil in our world the fact of evil is not arbitrary. We must remember that evil is an unavoidable consequence of free will and free will confers the profoundest imaginable benefits upon humankind.
5. The Conversion of the Hard-hearted
Inwagen shows us why Particular Horrendous Evils are unavoidable. But this leaves us to speculate on whether there is any positive reason why God permits them to occur. In Providence and the Problem of Evil, Richard Swinburne suggests one such a reason.
God loves evildoers and wishes for them to repent and be reconciled to Him—as discussed in my previous article. This fact, as Swinburne notes, provides a positive reason for God to allow particular horrendous evils: They make possible serious moral choices for people normally too timid or too hardhearted to make them.
This is a principle we see operating on a small scale in our everyday experience. A man too timid to defend a coworker from verbal abuse may be moved to defend him against physical abuse; a man too lazy to help an elderly neighbour struggling up the stairs with her shopping may be moved to rush to her aid if she takes a bad fall. But there exist people who, through the exercise of their own free will, have become hardhearted. And they may view physical conflict or an old lady falling down the stairs as an entertaining spectacle. To such people Particular Horrendous Evils offer the possibility of redemption.
Here Swinburne has in mind a prison guard who is moved to disobey orders by the terrible suffering of his captives; or a citizen who helps his neighbours to escape a death squad by hiding them in his basement—something which both men do at great personal risk despite being people who, in the normal course of life, were unmoved by the more moderate suffering of others. Some, while having no direct exposure to a horrendous evil, may be moved to make sacrifices in support of the victims or to campaign for reform; many others may be moved to discover and abandon their own subtle prejudices. And it is certainly plausible that some people of each type were caught up in the public outpouring of sympathy and solidarity that followed the Christchurch shooting.
This, I repeat, is an emotional subject and Swinburne’s argument needs to be read in its proper context. It is not here being claimed, simpliciter, that God is pleased to allow horrendous evils so that hardhearted people might be moved to compassion. My concern in this post has been to show that free will makes possible Higher-Order Goods which are more valuable than pleasure; that evil is an unavoidable consequence of free will; and that there is no non-arbitrary limit to the amount of evil God permits. Particular horrendous evils are therefore consistent with the existence of God. And when we think carefully about what further reason God may have for not preventing them, we find that they may also offer the last hope of moral redemption for the hardhearted.
 The objection goes back as far as the Greek philosopher Epicurus who asked: “Is God willing to prevent evil, but not able? Then he is impotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Whence then is evil?”
 As I argue here, omnipotence needs to be carefully formulated to allow for the constraints of logical possibility.
 In this post, for the sake of brevity, I am ignoring natural evil. However, I think that there is also a coherent solution to this problem which I discuss here.
 Inwagen’s fascinating article is available here: The Argument from Particular Horrendous Evils.