St. Augustine in fact studied rhetoric in his youth. Democracy makes something of a comeback in the Renaissance, which in part was fueled by the frantic serach for Greek and Latin books, so rhetoric does as well. Generally fragments of Aristotle's rhetoric were available, so the more complete Cicero was the hot seller, though it was not as good. In the Rennaissance, more than any time before or since, intelligence was judged by wit and style, so theory and catalogues of metaphor were developed. By understanding the basics of Aristotle's rhetoric, we can defend ourselves from underhanded propaganda.
Every situation has a speaker, a message and an audience.
By looking at these associations and evidence carefully, you can keep from being conned. But of course you can also use your knowledge of rhetoric for good. To really understand how important an understanding of rhetoric is, have a look at this typical freshman essay. Sometimes, however, the situation will demand that you shift your proportions. If the audience is hostile you you, you can try to show that you are a good person who has a good deal in common with them, but your best bet is to use facts, since they won't let you move them emotionally if they don't trust you.