How does this section of the book (Chapters 74-78) help Sophie to understand her grandfather and help the reader to understand Sophie better?

The reader learns an important aspect of Sophie's character in this section--the details of why she severed all contact with her grandfather. As a young college student, Sophie had stumbled upon a sex rite ceremony in which her grandfather was participating. Langdon explained the symbolism behind the ceremony to her in order for her to have a better understanding of her grandfather. This section of the book offers resolution to the previously unanswered question of what was so horrific that would cause Sophie to sever ties with her only living relative. The chapter also allows resolution for Sophie because her character learns about and begins to understand her grandfather.