Synthesized answer
The provided passages do not explicitly state the central thesis of the text.
However, based on the narrative presented, the passages describe a situation where Richard Curwen marries Eloise, the wealthy cousin of Antonia, the woman he is passionately in love with [1]. Richard's motivation for this marriage appears to be financial, as both he and Antonia are penniless and desire wealth [1]. The resemblance between Eloise and Antonia is noted as astonishing, which Richard seems to be leveraging [1].
The passages set up a premise of love, wealth, deception, and marriage driven by selfish desires, but the overarching thesis is not articulated.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Bride of Moat House by Norah Lofts Description: It began when he met Antonia. Richard Curwen fell in love—wildly, passionately—and the lovely Antonia returned his love. But Richard and Antonia were penniless. And too spoiled and selfish to live as ordinary mortals. They wanted the best. The very best. And so Richard married Eloise, Antonia’s frail but wealthy cousin. The resemblance between Eloise and Antonia was astonishing. In fact, most people couldn’t tell them apart. Which was exactly what Richard was counting on.