you can understand falsehood from the standpoint of truth but not the other way around, just as someone who knows light can understand darkness but not vice versa
From NT Wright's essay "Simply Lewis": reflections on a master apologist after 60 years.
My Oxford tutors looked down their noses if you so much as mentioned him in a tutorial. This was, we may suppose, mere jealousy: He sold and they didn’t. It may also have been the frustration of the professional who, busy about his footnotes, sees the amateur effortlessly sailing past to the winning post.
A very interesting essay posted over at Touchstone. NT Wright reflects on "Mere Christianity"
Lewis himself would have been the first to say that of course his book was neither perfect nor complete, and that what mattered was that, if it brought people into the company, and under the influence (or “infection”) of Jesus Christ, Jesus himself would happily take over—indeed, that Jesus had been operating through the process all along, albeit through the imperfect medium of the apologist.
And, as another imperfect apologist, I salute a great master, and can only hope that in sixty years’ time children yet unborn will say of me that, despite all my obvious and embarrassing failings, I too was used, in however small a way, to bring people under the influence and power, and to the love and kingdom, of the same Jesus Christ
There's a discussion of the article at Treaders.