Behind this question, almost always, is a particular face. The person who is suffering, or the person we loved who is gone, or the news story we cannot stop thinking about. Before any argument, the Christian answer has to begin where God's own answer began: not with words, but with the willingness to enter the suffering.
The question itself, though, is also worth examining. It assumes "evil" is a category we can speak meaningfully about — that some things are not just unpleasant but genuinely wrong. C. S. Lewis, before he was a Christian, used the cruelty of the world as his strongest argument against God. But he kept noticing he had to ask: where did he get this idea of just and unjust? "A man does not call a line crooked unless he has some idea of a straight line." The moral seriousness of the objection presupposes the very thing it tries to deny.
Free creatures are necessary for love
Love cannot be coerced. A God who wanted to be loved by genuine persons had to create creatures capable of choosing him — which means capable of refusing him. The possibility of moral evil is the price of the possibility of moral good. A world with no possibility of cruelty is also a world with no possibility of courage, mercy, or the kind of sacrificial love that has made even hostile observers weep.
God uses what he permits
Not every instance of suffering produces an obvious good, and Christianity does not pretend otherwise. But the Christian claim is that no suffering is finally wasted. J. Warner Wallace observes that some of the deepest goods in the world — forgiveness, perseverance, the love that bears another's burden — require an evil context to exist at all. And the Eastern Fathers have always taught that God transforms what he permits. "The wood of the Cross became the Tree of Life" — the very symbol of human cruelty became the means of cosmic healing.
God answered evil personally
This is what makes the Christian answer unlike any other. Christianity does not claim to have a clean argument that lets God off the hook. It claims that God himself entered the suffering and bore it from inside. The Cross is not God's theory; it is God's answer in person. Whatever final theodicy might be, we know God is not aloof from suffering — he was nailed to it.
The Orthodox Paschal hymn calls it "the death of death." The world's suffering was taken into God himself and transfigured. It is still real; it still wounds; we still weep. But it does not have the last word.
For the one who is suffering
The book of Job ends without an explanation. It ends with a Person. So does Christianity. The deepest answer to suffering is not an argument — it is the One who wept at the tomb of his friend even though he was about to raise him (John 11:35). He weeps with us before he wipes the tears away.
As Tim Keller wrote, "Christianity alone among the world religions claims that God became uniquely and fully human in Jesus Christ — and therefore knows our suffering from the inside." That is not a complete answer to the philosophical question. It is something better than an answer. It is a Person to suffer with.