If God is good and all-powerful,
why is there suffering?

Lay the three claims out plainly. God is all-powerful, so nothing stops him from acting. God is perfectly good, so he wants to prevent needless suffering. And suffering is real, vast, and often falls on those who did nothing to deserve it. Any two of these sit together comfortably. Getting all three to hold at once is the problem, and every serious response is an attempt to loosen one claim without letting go of it.

The logical problem — a flat contradiction

The strong version, pressed hard by J. L. Mackie, claims that God and evil are logically incompatible: if the two ideas contradict, then like a square circle, both cannot exist. Most philosophers now think this version fails, because the believer only needs to show a possible reason God might allow evil, not a likely one. That is the job the free-will defense does, and it does it well enough that the logical problem is widely considered answered.

The evidential problem — the harder one

The weaker-sounding version is the one that bites. It grants that God and evil could coexist, then argues from the sheer amount and apparent pointlessness of suffering that God is unlikely. William Rowe's example is a fawn burned in a forest fire, dying slowly and alone, its agony witnessed by no one and teaching no one anything. Multiply that by every hidden cruelty in history, and the claim is not that God is impossible but that a good God looks improbable.

The free-will defense

The most rigorous reply, refined by Alvin Plantinga, argues that a world of free creatures is worth more than a world of puppets, and that real freedom makes real evil possible. God cannot force free beings to always choose the good without erasing the freedom that made them valuable. So moral evil, the cruelty people do to each other, is the price of a good worth paying. The strain: it says little about suffering no human chose, like disease, earthquakes, and animal pain.

Soul-making

John Hick, drawing on the early theologian Irenaeus, argued that the world is not meant to be a comfortable resort but a place that grows souls. Courage, compassion, and endurance can only exist in a world with real hardship to meet. Suffering is the friction that forms character. The strain: some suffering seems to crush people rather than grow them, and infants and animals gain no character from it.

Skeptical theism

A more modest reply concedes we cannot see a reason for much suffering, then denies that our not seeing one means there is none. A finite mind looking at an infinite plan is like a child watching a surgeon and seeing only cruelty. The strain: pushed too far, it can undercut all moral reasoning, since it invites us to doubt our judgment about what is good whenever it is convenient.