Writing a novel in the form of a letter or a diary (think Bridget Jones) is a tried and true device for writing your novel.
DEAR AMERICAN AIRLINES by Jonathan Miles uses the letter device.
“â€˜Dear American Airlines,â€™ Jonathan Milesâ€™s fine first novel, takes the form of a letter to the titular air carrier, which has stranded Benjamin R. Ford, the bookâ€™s middle-aged protagonist, in Oâ€™Hare Airport on the way to his estranged daughterâ€™s wedding.”
So if you’re writing a novel and are stuck, write a chapter or two in the form of a letter. It’s a fascinating way to reveal more of your character and help him come alive for the reader – and for you.