Expository writing means putting ideas in context. Exposition is the information a writer gives his or her readers so that they can understand the meaning and significance of the writer’s conclusions. So, writing in an expository mode means figuring out what facts and ideas you need to convince your reader that what you have to say really matters.
By teaching students how to do this, we show them how to take the mass of information and ideas that they encounter in their college classes, figure out how those ideas should matter to them, and express that understanding to someone else. Basically, we teach students to be active participants in their own educations.