Today is the feast day of St. John of the Cross. His written works can be found online here, including Dark Night of the Soul. Thomas Merton wrote an essay on him. It says, in part,
Sanctity can never abide a merely speculative solution to the problem of suffering. Sanctity solves the problem not by analyzing but by suffering. It is a living solution, burned in the flesh and spirit of the saint by fire. Scripture itself tells us as much. "As silver is tried by fire and gold in the furnace, so the Lord trieth hearts" (Prov 17:3).Merton offers St. John of the Cross as one who can give us an answer to the problem.