Juliet writes to Sidney, begging him to send her to Guernsey. She says she's read as much as she can about the island and conducted some interviews with soldiers in London, but there's only so much she can learn by reading. Juliet says she wants to learn the stories of the people who were there and possibly write a book about it all.
Juliet's desire to go to Guernsey indicates that while reading can connect people, the books themselves only go so far. In order to build a true friendship, it's necessary to get to know others more intimately than just through books.