In the sixth chapter, “Human Pain,” from The Problem of Pain (1940), C.S. Lewis writes:
We can rest contentedly in our sins and in our stupidities; and anyone who has watched gluttons shovelling down the most exquisite foods as if they did not know what they were eating, will admit that we can ignore even pleasure. But pain insists upon being attended to. God whispers to us in our pleasures, speaks in our conscience, but shouts in our pains: it is His megaphone to rouse a deaf world. A bad man, happy, is a man without the least inkling that his actions do not “answer”, that they are not in accord with the laws of the universe.
No doubt Pain as God’s megaphone is a terrible instrument; it may lead to final and unrepented rebellion. But it gives the only opportunity the bad man can have for amendment. It removes the veil; it plants the flag of truth within the fortress of a rebel soul.