How are letters important to Joan and Imogen in the novel, Love & Saffron?

Imogen and Joan's letters are a representation of memories and the growth they made together. This is why Imogen saved all of them to send to Joan should she pass away. It is also why she wrote a special letter to Joan before Imogen's surgery as she understands that letters have the power to comfort and encourage those who receive them. It is also a very personal thing, as pointed out by Imogen when she mentions the involved process of handwriting, addressing, and sending the letter to those one cares about. These letters are at the heart of Imogen and Joan's lives and inspire them to live for each other, especially after Imogen passes away and Joan must decide what kind of life she wants to have.