This occurs in chapter 5. Miss Maudie and Scout are having a talk about Boo Radley. Scout wonders if Boo might just be dead in the house because he never comes out. Miss Maudie tells her that certainly isn't the case because Boo hasn't been carried out yet and buried. Miss Maudie goes on to tell Scout that Scout has already heard all the stories of Boo. Mr. Radley is a "foot-washin'" Baptist, which means he was very strict about the bible. Maudie criticizes Mr. Radley about this a little and Scout still struggles to understand. I think Maudie is suggesting that Boo's been kept inside for so long because his father said he would take care of the major "sin" Boo had commited earlier. Boo just probably got used to being inside and not being allowed to associate with society that now it is comfortable for him.