Suffering is the door. The Buddha opened his teaching with it (Dukkha); Christianity centers on a cross; Judaism makes exile and return its grammar; Islam is literally “submission” to what is. Traditions differ on suffering’s cause, meaning, and remedy — but none ignores it.
See Dukkha for the Buddhist analysis; theodicy for the classical theistic problem of reconciling evil with a good God; Compassion for the cross-tradition response.