Perhaps it is helpful to think of an essay in terms of a conversation or debate with a classmate. If I were to discuss the cause of the Great Depression and its current effect on those who lived through the tumultuous time, there would be a beginning, middle, and end to the conversation. In fact, if I were to end the exposition in the middle of my second point, questions would arise concerning the current effects on those who lived through the Depression. Therefore, the expository essay must be complete, and logically so, leaving no doubt as to its intent or argument.
The first sentence of the concluding paragraph uses the principal words from the quotations from each paragraph of the body of the paper. This summarizes those three paragraphs. The second and third sentences provide observations which can also be considered a summary, not only of the content of the paper, but also offers personal opinion which was logically drawn as the result of this study. The last sentence returns to the Edgar Allan Poe-Stephen King relationship that began this paper. This sentence also provides a "wrap-up" and gives the paper a sense of finality.