For a book like The Wife of Martin Guerre, the historical context of the book is very important, since in this case, the author penned the novel to make a very specific point. She is hoping to illustrate a scenario when circumstantial evidence couldn't be trusted. To do this, Martin Guerre's story became useful and meaningful. Martin's long absence from his home and from his role as husband has left his wife in the strange predicament of misremembering his appearance. When a similar-looking man comes along as an imposter claiming to be Martin, the wife takes the bait. The novel is about the capacity of the wife to deceive herself, since she benefits from the lie.
The way she benefits from the lie is that in an attempt to convince her that he is the real husband, the imposter does an even better job at marriage that Bertrande's real husband ever did. She remembers enough about him to know that she doesn't really want the real Martin to come home.
When he does, she has a decision to make. She admits to him that she was deceived by the imposter, which he regards as unforgivable, which makes sense given Bertrande's account of his temperament, but more importantly, it means that Bertrande's intuition was right all along. Secretly, she knew the truth and pretended to be deceived by the lie for expedience, because she liked the way the imposter made her feel. This is the central meaning of the narrative, since it show's Lewis's point of view about the nature of subjectivity, and consequently, about the use of circumstantial evidence in a court of law.
