Emerson’s Nature is an essay. The beginning of the 19th century, in particular, had an explosion of essayists writing in English, so by the time Nature was written in the 1830s, Emerson would have been familiar with the virtues of the essay as a persuasive genre. He was particularly inspired by the Scottish essayist Thomas Carlyle.
Many of Emerson’s essays and lectures were designed to lay out the foundations of the transcendentalist movement. A key feature of Transcendentalism is the emphasis on mystical and divine—or, in other words, transcendent—states as something desirable. This text focuses on exploring the awe that nature inspires, zeroing in on the feeling of being elevated to another plane of existence. Such feelings are supposed to give rise to unique insights into the world and intense moments of joy.
Emerson likely chose an essay as the genre for Nature to communicate transcendentalist ideas clearly without giving up the poetic prose that inspires feelings in the reader. The essay has the advantage of being straightforward, and this is what sets Nature apart from many of the other contemporary transcendentalist works at the time—most of which were poetry focused primarily on inspiring a feeling of awe for the natural world rather than communicating ideas in a way that would maximize understanding. However, in the essay format, unlike perhaps a dry manifesto or philosophical proof, Emerson still can preserve the kind of poetic language that inspires the moods that transcendentalists believe are key to grasping meaning and truth.