Stories generally provide entertainment, but some have morals embedded in them. In such cases, the writer's purpose is to ... Entertain, Pacify, Instruct, chide ... the audience, not just enthrall them. These stories are also known as ... Frame, Didactic, Comic, Deceptive ... tales

Instruct ... didactic.

The writers are offering moral lessons. Think of the writer as a teacher giving a lesson on math problems. What's another way of saying that? The teacher instructed the class on arithmetic problems.

Didactic means "intending to teach." So that's the only option that works.