You will do well with Mr. Emerson's work if you remember these insights about the ideology of his time period, which was Transcendentalism. Here are the main criteria:
a. All men are infused with divinity, and are capable of great growth and fulfillment if they listen to their inner voice, rather than the dictates of society, government, or religious institutions.
b. Truths that were blindly followed in the past have no relevance to today's realities; you must find your own truth by following your conscience.
c. Man will discover his true 'self' when he walks into Nature, and observes its transcendent beauty and power; God instills the same divinity in all of Nature that He does in man, and in Nature's solitude, man will find truth.
Transcendental writers did not organize their paragraphs in the DEDUCTIVE manner that we do nowadays--i.e., beginning by a topic statement, then providing evidence. Instead they proceeded INDUCTIVELY, often beginning with an example or riveting detail. Eventually the paragraph will build to a very powerful, memorable statement, often a short or blunt statement full of metaphoric language or rhetorical power. For example, in the opening paragraph of "Nature," the sentence embedded within the text beginning "One might think" captures the main idea of the paragraph. In paragraph 3, the blunt sentence starting 'But none of them...' encapsulates the main idea of that paragraph.
Emerson's writing can be densely textured and also very abstract, but if you find that one 'nugget' sentence within the paragraph, you'll be well on the way to seeing the main idea.