In order to express the gratitude toward nature that he believes his age lacks, Emerson uses a reverent tone to elevate Nature (and nature) to the sublime. Emerson believes that the majority of people, especially adults, are unable to truly see nature as the miraculous healer and teacher that it is. Most ignore or mindlessly project their internal state onto nature, which for Emerson is a deadly mistake that prevents the majority of people from reaping the benefits that nature has to offer. Emerson uses a reverent tone because he wants humanity to be able to reach its full potential by seeing nature for what it truly is: useful.
However, he also sets nature up as a servant for man, which may seem contradictory to the reverent tone he uses. One typically reveres things that are holier or more powerful than them. On the other hand, one typically believes that only things less holy or less powerful than them should be subservient. This contrast is not necessarily a contradiction for Emerson, since he implies that divinity (particularly Jesus) also humbly serves.
Additionally, Emerson uses a reverent tone to make the reader see the individual as something worthy of respect. Painting the individual as something worthy of respect elevates the value of contemporary personal experience over the traditions of ages past. If the individual is valuable, then so are their thoughts, feelings, and experiences. If those thoughts, feelings, and experiences are just as valuable and likely to be true as the edicts of one’s religion, culture, state, etc., why not trust one’s own judgment over external logic? This argument is one of the main theses of the transcendentalist school.
While nature and the individual are unappreciated, reverence toward God is expected. Readers would have been accustomed to God being addressed with a reverent tone. Therefore, using the same tone to discuss all three further solidifies the interconnectedness between nature, the individual, and divinity.