Fifty years ago today, Martin Luther King, Jr., delivered his “I Have a Dream” speech as the March on Washington drew to a close. The nation was wowed. But as good as the speech is, to appreciate the full range of King’s gifts, you must read the letter from Birmingham jail he wrote five months earlier. As an example of persuasive writing, it’s top-drawer. It matches the “I Have a Dream” speech in imagery and musicality, but surpasses it in rhetorical genius.