I am currently re-listening to Dorothy Sayers's Clouds of Witness in audiobook, and enjoying the Dowager Duchess, who has always been one of my favorite characters, and is one of the few examples of correctly writing a person so intelligent that she has difficulty communicating with other people.
"He said what he thought," said Mary. "Of course, Lord Mountweazle, poor dear, doesn't understand that the present generation is accustomed to discuss things with its elders, not just kow-tow to them. When George gave his opinion, he thought he was just contradicting."
"To be sure," said the Dowager, "when you flatly deny everything a person says it does sound like contradiction to the uninitiated. But all I remember saying to Peter was that Mr. Goyles's manners seemed to me to lack polish, and that he showed a lack of independence in his opinions."
"A lack of independence?" said Mary, wide-eyed.
"Well, dear, I thought so. What oft was thought and frequently much better expressed, as Pope says—or was it somebody else? But the worse you express yourself these days the more profound people think you—though that's nothing new. Like Browning and those quaint metaphysical people, when you never know whether they really mean their mistress or the Established Church, so bridegroomy and biblical—to say nothing of dear S. Augustine—the Hippo man, I mean, not the one who missionized over here, though I daresay he was delightful too, and in those days I suppose they didn't have annual sales of work and tea in the parish room, so it doesn't seem quite like what we mean nowadays by missionaries—he knew all about it—you remember about that mandrake—or is that the thing you had to get a big black dog for? Manichee, that's the word. What was his name? Was it Faustus? Or am I mixing him up with the old man in the opera?"
"Well, anyway," said Mary, without stopping to disentangle the Duchess's sequence of ideas, "George was the only person I really cared about—he still is. Only it did seem so hopeless. Perhaps you didn't say much about him, mother, but Gerald said lots—dreadful things!"
"Yes," said the Duchess, "he said what he thought. The present generation does, you know. To the uninitiated, I admit, dear, it does sound a little rude."
Peter grinned, but Mary went on unheeding.
The quotation from Pope is actually (from "An Essay on Criticism", of course):
True wit is nature to advantage dress'd,
What oft was thought, but ne'er so well express'd,
Something, whose truth convinc'd at sight we find,
That gives us back the image of our mind.
However, as is generally the case with intelligent literary use of quotation, the relevance of the quotation lies partly in what is not quoted; the passage immediately prior to this passage is about poetic conceits; Pope is criticizing poets who rely on striking conceits rather than saying things in a way that's "just and fit", with "modest plainness" that depicts the natural truth with artistic grace. The Dowager is implicitly criticizing the young for not caring how things are said, but her modification of the quotation is an even harsher put-down of Mr. Goyles, who says things that oft were thought but elsewhere are much better expressed.
However, Pope's criticism of conceits -- again, only explicit in the part that she is not quoting -- leads her to think of Browning and the Metaphysicals, who are poets famous for their poetic conceits. And the criticism that "you never know whether they really mean their mistress or the Established Church" is a hilariously good jab at the Metaphysicals; because they are (especially Donne) very "bridegroomy and biblical". But the "bridegroomy and biblical" conceits of the Metaphysical poets leads her to think of the passage in St. Augustine's Confessions in which he talks about the smooth-talking Manichaean bishop, Faustus, and she carefully makes clear that she means Augustine of Hippo, not Augustine of Canterbury, who missionized England, although not in the way that is meant when we speak of the work of the Church Missionary Society in the local parish of the Church of England. Augustine reflecting on his interest (as a rhetorician) in Faustus mentions, among other things, that he was already beginning to learn that truth and presentation come apart, and among the several examples he gives of this is that things are not necessarily true merely because they are rudely expressed, which is pretty clearly what the Dowager Duchess has in mind.
Even her potential confusions are theme-relevant. She worries she is confusing Faustus the Manichaean with Faust, in Charles Gounod's best-known opera, Faust, but this ties in to the theme, because Gounod's Faust was famous for being unusually good in its presentation -- modest and simple but powerfully expressed. Her confusion between mandrake and Manichee likewise also ties into the theme. A mandrake, according to legend, screams unbearably when pulled from the ground (usually with the help of a black dog), which ties back into the rudeness of the younger generation.
