I agree with you that the defense of the novel passage is a wonderful piece of writing, but to me it also seems a bit out of place: it stops the action dead and, although the sentiments are clearly relevant to the themes and plot of NA, the passage has a telling-and-not-showing quality that, I suspect, may give us a clue to JA's relative artistic immaturity in this book. The narrator in NA is a much more intrusive presence than in the other novels, where the narratorial voice seems to grow more organically out of the social world of the characters. Still, the NA narrator's voice is so snarkily funny that I'm not sure this is, on the whole, a bad thing.