Now it is quite certain that all these expressions [fire, darkness, and chains] are intended to suggest something unspeakably horrible, and any interpretation which does not face that fact is, I am afraid, out of court from the beginning. But it is not necessary to concentrate on the images of torture to the exclusion of those suggesting destruction and privation. What can that be whereof all three images are equally proper symbols? Destruction, we should naturally assume, means the unmaking, or cessation, of the destroyed. And people often talk as if the "annihilation" of a soul were intrinsically possible. In all our experience, however, the destruction of one thing means the emergence of something else. Bum a log, and you have gases, heat and ash. To have been a log means now being those three things. If soul can be destroyed, must there not be a state of having been a human soul? And is not that, perhaps, the state which is equally well described as torment, destruction, and privation? You will remember that in the parable, the saved go to a place prepared for them, while the damned go to a place never made for men at all. (Matt. 25:34, 41) To enter heaven is to become more human than you ever succeeded in being in earth; to enter bell, is to be banished from humanity. What is cast (or casts itself) into hell is not a man: it is "remains."

source: C. S. Lewis, The Problem of Pain, chapter 8 tags: Hell