This is one of those quotes that's probably been posted on Catholic blogs a bajillion times, but I'd never seen it before, so here it is, 'cuz I like to share:
I say from the nature of the case, if Literature is to be made a study of human nature, you cannot have a Christian Literature. It is a contradiction in terms to attempt a sinless Literature of sinful man. You may gather together something very great and high, something higher than any Literature ever was; and when you have done so, you will find that it is not Literature at all.
John Henry Cardinal Newman, as quoted by Graham Greene, as quoted by Edward Short here.