For whatever reason I feel compelled to write on Emerson's description of Thoreau's incredibly acute knowledge of the natural world.
Doubtless, Thoreau was indubitably the greatest naturalist of the 20th Century, and perhaps one of the most thorough in all of American history. Unencumbered by social constraints, expectations on himself, and care for the mirth of his fellow man, Thoreau pursued his passion for all things natural, beautiful and of God's most intimate creation without reservation. He tuned himself to the cycles of the natural world. He became so self-aware - in regards to his personhood in respect to nature - that nothing was less natural to him than removing oneself from the hyper-alert, congruent natural life. Living by the cycles of the Earth fueled Thoreau's passion for studying the Earth. He was brilliant because He chose to be Himself - a naturalist, a writer, a soul free from the societal constrictions of social conventions. Emerson recognized this unique brilliance in his heady, reclusive friend, and in turn, drew strength from Thoreau's unbridled pursuit of his passion.
A great lesson for us all. Drop expectations, follow what you know to be true, honest and empowering and live life with unbridled passion, like Thoreau.