For what reasons did medieval writers use allegory?

In chapter 3, scout criticizes her classmate, walter cunningham, for asking for molasses and then pouring it on his vegetables and meat while he was a guest at the finch home. in this scene, what does the author’s use of flashback in a first person point-of- view narration achieve?

Could someone me with this question?

The room was gaudy with its leather couch and purple walls