What are the speakers mainly discussing?

Listen to a conversation between a student (S) and his American literature professor (P).
P: Did you decide to do your paper on Thornton Wilder the novelist, or Thornton Wilder the playwright? He was both, you know?
S: Oh, the novelist, for sure, l just finished reading his book The Bridge of San Luis Rey and I really liked it. I know why it’s so popular. I’m just not sure what to focus on in my paper.
P: Why do you like the book?
S: l like the way Wilder uses different characters to illustrate different ideas. It’s like they’re not realistic human beings. The characters are more like types, you know?
P: That’s a good observation. Many novelists write realistic fiction. They shape their novels with the intention of portraying actual situations, but if that’s not Wilder’s goal, then what, would you say, is he up to?
S: I think he’s trying to teach something, something philosophical kind of, something that’s true for everybody everywhere.
P: You mean a moral lesson, like a fable? Alight, that’s a good start. So we have a 20th century North American author telling a fable that’s set in 18th century Peru. I’m curious... does that seem remarkable to you at all?
S: No, not really. Probably some people just like writing about the past or about places they’ve been. I figured maybe Wilder had visited Peru and thought it would be a great setting for a novel.
P: Interesting theory, yet Wilder hadn’t visited Peru when he wrote The Bridge of San Luis Rey. I’d like to suggest another possibility to you that his choice of setting was intentional, so he could do just what you mentioned.
S: So if you want to teach a moral, it’s better to set your novel someplace you’ve never actually been, so you’re not distracted by what you know about the place, what you remember.
P: Right. Also, a setting in the past has the same effect; plus, it gives you a certain amount of distance from your characters, but Wilder received some harsh criticism for doing that.
S: He did?
P: Yes. You see, Wilder avoided contemporary settings in most of his novels. He was actually accused of being out of touch with the real world and therefore not an important author, because he didn’t write about contemporary life and contemporary problems.
S: What kind of sense does that make? Like you said, he probably stayed away from contemporary settings, so he could concentrate on the philosophy, the moral truths.
P: There was quite a debate over it at the time. When you do your paper, you’ll need to do a bit of research into that and one other thing you’ll need to research. Well, I also recommend you take a look at Wilder’s comic novel Heaven’s My Destination. That book did, in fact, draw in many ways on elements of his life, and yet some people think it has a lot in common with The Bridge of San Luis Rey, so you might have the basis there for a fruitful comparison.