What is the purpose of reading over your essay?

To expose. As you can see in the root of the Word, expository, itself.

In layman's terms, it's basically to tell the reader about a problem or something interesting that he has never learned or heard about before, update the reader on something he may have already known, or state facts including minimum bias about something.

Expository essays are also descriptive, elucidative, exegetic, explanatory,