Think of it this way. As the writer of an essay, you're essentially a lawyer arguing in behalf of a client (your thesis) before a judge (the reader) who will decide the case (agree or disagree with you). So, begin as a lawyer would, by laying out the facts to the judge in the way you think it will help your client best. Like lawyers in court, you should make an "opening statement," in this case, an introduction. Then review the facts of the case in detail just as lawyers question witnesses and submit evidence during a trial. This process of presentation and cross-examination is equivalent to the "body" of your essay. Finally, end with a "closing statement"—that is, the conclusion of your essay—arguing as strongly as possible in favor of your client's case, namely, your theme.
Elements toward building a good persuasive essay include * establishing facts to support an argument * clarifying relevant values for your audience (perspective) * prioritizing, editing, and/or sequencing the facts and values in importance to build the argument * forming and stating conclusions * "persuading" your audience that your conclusions are based upon the agreed-upon facts and...
to follow when writing a conclusion for their persuasive essays.
These are not arbitrary requirements. Introductions and conclusions are crucial in persuasive writing. They put the facts to be cited into a coherent structure and give them meaning. Even more important, they make the argument readily accessible to readers and remind them of that purpose from start to end.