From the Business of Heaven:
It is a terrible thing that the worst of all the vices can smuggle itself into the very centre of our religious life. But you can see why. The other, and less bad, vices come from the devil working on us through our animal nature. But this does not come through our animal nature at all. It comes direct from Hell. It is purely spiritual: consequently, it is far more subtle and deadly. For the same reason, Pride can often be used to beat down the simpler vices. Teachers, in fact, often appeal to a boy’s Pride, or, as they call it, his self-respect, to make him behave decently: many a man has overcome cowardice, or lust, or ill-temper by learning to think that they are beneath his dignity—that is, by Pride. The devil laughs. He is perfectly content to see you becoming chaste and brave and self-controlled provided, all the time, he is setting up in you the Dictatorship of Pride—just as he would be quite content to see your chilblains cured if he was allowed, in return, to give you cancer. For Pride is spiritual cancer: it eats up the very possibility of love, or contentment, or even common sense.
Self-righteousness is one of the biggest enemies of western Christians (including me). We must root it out and see it crucified.