If God is good, why does He allow suffering?

This is the oldest question, and the Catechism does not dodge it: "To this question, as pressing as it is unavoidable and as painful as it is mysterious, no quick answer will suffice" (CCC 309). But there is an answer, and it has several parts.

Freedom. God made creatures capable of love, and love requires freedom, and freedom can be misused. Most suffering in the world comes from human sin: war, cruelty, greed, neglect. God could have made a world without free beings; He judged that a world with love in it, and therefore with the risk of evil, was worth more (CCC 311, 1730-1733).

A world in journey. Creation is not finished; it is "in a state of journeying toward its ultimate perfection" (CCC 310). Physical evils, earthquakes, disease, death, belong to a world that is good but not yet complete. Adam's sin broke the harmony of creation (Rom 8:20-22), and we live in that fracture.

The greater good. God "permits evil in order to draw forth some greater good from it" (CCC 312; St. Thomas). Joseph told his brothers, "You meant evil against me, but God meant it for good" (Gen 50:20). The supreme case is the crucifixion: the worst evil in history became the source of the world's salvation.

The real answer is a Person. God did not send a philosophy. He came down. Jesus wept at Lazarus's tomb, sweated blood in the garden, and cried, "My God, why have you forsaken me?" Whatever you suffer, He suffered first, and He is with you in it (Heb 4:15). And He rose, which means suffering does not have the last word. "The sufferings of this present time are as nothing compared with the glory to be revealed" (Rom 8:18).

What to do with it. Catholics "offer it up": unite suffering to Christ's, so that it becomes redemptive for others (Col 1:24; CCC 1505, 1521). Suffering that is offered is never wasted. Ask the saints who suffered most, Thérèse dying of tuberculosis at twenty-four, Maximilian Kolbe in the starvation bunker, and they will tell you that in the Cross they found love.