Well, Emerson uses abstract words like "heroism, contradiction, and secret impulse of an individual's character." When Emerson says, "just and wise men take umbrage at his act," and "clean contrary to a sensual prosperity," he's really challenging his readers to think about their own ways of thinking about things. Just because "everybody knows" something and it's "what's in the books." doesn't mean we can't think about something in a new way. It might be a better way, and it takes heroic vision to go against popular wisdom.
Thoreau is not nearly as abstract, but his use of "this my native town" instead of "hometown" or "place of my birth" is a form of more elevated diction. Instead of something like "nature keeps going, and children can still see things like I saw as a child," Thoreau says "preparing another aspect for new infant eyes." His flowery diction really takes off when he writes,