Answer:
- move a story forward
- share internal thoughts and feelings of other characters
- reveal perspectives and experiences of other characters
- add to the suspense of a story
Step-by-step explanation:
A card can reveal a lot of a plot. These revelations can make a story move more fluidly forward, share secrets, inner thoughts, expectations and ambitions of the characters. In addition, these revelations can bring a mystery and a suspense to the story.
In short, letters can be devices that can be used by the author as a way of revealing something about the character. This revelation can not be included in a dialogue, so the letter is the best option.