Writing is a window to the soul in Ella Enchanted. Ella's and Char's letters reveal confident and clever people behind the pens, while the glimpses we get of Hattie's and Olive's letters (thanks to Ella's magical book) reveal them to be dull and greedy. The fact that much of Ella and Char's courtship takes place through letters is significant; it's like the fantasyland equivalent of flirting through texting and IMing (but with better spelling and grammar). Still, writing can be a double-edged tool: Ella is able to fool Char into thinking she never really loved him with a shrewd trick of her pen. Shakespeare's got nothing on this girl.
In Kyrria, at least, the pen is mightier than the sword.
Had they been courting in person instead of by letter, Ella and Char wouldn't have gotten to know each other so well.