Passage Summary: Muriel thinks a novelist needs to write about many different things to be great, but John disagrees, saying a writer can be great just by exploring one theme very deeply.

Reasoning: Muriel claims that a writer must have varied subject matter to be considered great, while John argues that diversity of subject matter is not a requirement for greatness.

Analysis: To identify the point at issue, we apply the 'Agree/Disagree' test to the speakers' criteria for literary greatness. Muriel explicitly states that Favilla isn't great because her subject matter isn't varied enough, implying that variety is a necessary condition. John explicitly rejects this, stating a great writer 'does not need' diversity in subject matter. Therefore, the central dispute is whether having a wide variety of subject matter is a necessary requirement for being a great writer.