The final paragraph of your essay is where you will summarize your argument and present the reader with your ultimate conclusion. The standard format for an essay's conclusion is to restate the thesis, and then concisely demonstrate how your supporting points have proven your original assertion. It is important that the conclusion of your essay be strong and definitive. In the end, you want to present your reader with a coherent and concise essay that demonstrates your knowledge of the topic at hand, and your ability to reason and argue clearly and with precision.
I would say that the applicant who wrote the “Imagine” essay didn’t get due to the essay’s flat prose, poor organization, and questionable grammar, not its subject matter. The song was not sung “by the show,” but by the characters on the show. The sentence “When I watched this episode while the deaf adolescents were singing it, and soon joined by another glee club, it surprisingly affected me…” is just an incredible mess. He didn’t watch “while” they were singing; it should be “were joined by;” and “surprisingly affected me” is a terribly clumsy construction. How about: “As I watched another glee club join the deaf adolescents in singing the song during this episode, I was surprised by how much it affected me.” Not all applicants will be strong writers, but all need to show at least a basic grasp of how to communicate a thought.