TRANSMISSION OF CULTURE: While a history textbook or transcripts of court trials, or newspapers can tell us the facts and events of a society, nothing can share the feelings or beliefs like literature does. In literature we see the struggles and triumphs of various societies in addition to how people responded to them. People's morals and values are often portrayed through literature.
ART OF COMMUNICATION: Some people express themselves well visually, others verbally, and yet others with the written word that has had opportunities for editing and several drafts.
SCIENCE OF COMMUNICATION: Often, an author will have a significant feeling on an issue that they wish to communicate. To persuade people to think or feel similarly, they might entertain, use reverse psychology (like a dystopia), or blatantly describe the issue with many literary devices.
A word on literary devices: For everyone, there are different comparisons or hyperboles that speak to us. An author of a literary piece can use many to convey their point.