Pivotal moments in U.S. history are indelibly marked by the sermons of the nation's greatest orators. America's Puritan founder John Winthrop preached about "a city upon a hill", a phrase echoed more than three centuries later by President Ronald Reagan in his farewell address to the nation; Abraham Lincoln's two greatest speeches have been called "sermons on the mount"; and Martin Luther King Jr.'s "I Have a Dream" oration influenced a generation...