You can’t go on “seeing through” things forever. The whole point of seeing through something is to see something through it. To “see through” all things is the same as not to see.

Whatever men expect, they soon come to think they have a right to; the sense of disappointment can, with very little skill on our part, be turned into a sense of injury. (senior devil speaking)

You will say these are very small sins... [But] it does not matter how small the sins are provided that their cumulative effect is to edge the man away from the Light and out into the Nothing. Murder is no better than cards if cards can do the trick. Indeed, the safest road to Hell is the gradual one--the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts

Golly,' said Edmund under his breath, 'He's a retired star.

It is that of an unsatisfied desire which is itself more desirable than any other satisfaction.

He (the devil) always sends errors into the world in pairs--pairs of opposites...He relies on your extra dislike of one to draw you gradually into the opposite one. But do not let us be fooled. We have to keep our eyes on the goal and go straight through between both errors. We have no other concern than that with either of them.

and the whole forest would give itself up to jollification for weeks on end.