The Problem of Evil and Suffering
If God is all-powerful and all-good, it would have created a universe in the same way it created heaven: with free will for all, no suffering and no evil. But evil and suffering exist. Therefore God does not exist, is not all-powerful or is not benevolent (good). A theodicy is an attempt to explain why a good god would have created evil and suffering. The most popular defence is that it is so Humans could have free will. However the entire universe and the natural world is filled with suffering, violence and destruction so any Humanity-centric explanation does not seem to work.
Click on the book cover to open the chapter on the Problem of Eveil from the AQA text book