The Brothers Karamazov by Fyodor Dostoevsky (1880)

Two brothers sit in a tavern on a freezing afternoon, and the younger one listens while the elder calmly takes the universe apart. Ivan does not deny that God exists. He simply returns his ticket to a creation whose final harmony is purchased with the tears of one tortured child, and asks how any heaven could be worth that price. It is the most devastating case against faith ever written, and Dostoevsky, dying as he worked, was brave enough to let it stand stronger than any answer he could give. Then he answers it anyway, not by refuting Ivan but through Alyosha, the gentle novice who meets the same darkness and keeps loving. Around them the story closes like a trap: their monstrous father murdered, the passionate Mitya in the dock for a crime that may not be his. Love in action, the book knows, is a harsh and dreadful thing beside love in dreams. You will finish it still arguing which brother was right, and you will never quite stop.