Ralph Waldo Emerson was a nineteenth century American philosopher and scholar, as well as a very influential writer, who influenced many other American writers in decades to come. This happened because he himself was a man of character, definitive Christian faith, firm personal beliefs and obvious integrity. His treatise on nature, published anonymously in 1836 (492), demonstrates all of that, starting in the first introductory lines of the essay, where Emerson writes:
Our age is retrospective. It builds the sepulchres of the fathers. It writes biographies, histories, and criticism. The foregoing generations beheld God and nature face to face; we, through their eyes. Why should we not also enjoy an original relation to the universe? (492)
These introductory lines of both the actual essay and just its "Introduction", demonstrate Emerson's knowledge of the Bible as a true Christian should, as well as his somewhat hidden negative attitude of his fellow people - the specific passage in the Old Testament that talks about sepulchres uses it in a negative allegory regards the poor condition Jewish faith of that time - and therefore Emerson's use of the sepulchres in the second sentence of his essay is practically the first hint of the criticism of the American society of his time that will manifest in the main body of "Nature".
In "Introduction" of "Nature", however, Emerson is not talking about the human society, as he will start to in the chapter II of his essay, "Commodity". Here he, rather, talks about, or prepares to talk about, of the wonders of nature, which he, as a good Christian, puts into a positive light of a theologically-related event:
Seen in the streets of cities, how great they are! If the stars should appear one night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God which had been shown! However, every night come out these preachers of beauty, and light the universe with their admonishing smile. (493)
The above quote typifies Emerson's style - the one used to write "Nature", at any rate. It is still a bit mild as compared to the latter chapters where Emerson writes and compares things of nature and features of human society, described simply as Commodity, Beauty, Language and Discipline (495).
Right now, though, just like every other time, when Emerson talks about wild nature, he always uses words that manage to convey the sombre and simple significance of nature's works, but every time he talks about human society and similar topics, he uses a much more casual and even somewhat sarcastic speech: "Miller owns this field, Locke that, and Manning the woodland beyond" (494) contrasts quite sharply with, for example, "The flowers, the animals, the mountains, reflected in all the wisdom of his best hour, as much as they delighted the simplicity of his childhood." (494)
This is what is so interesting about the passages that were quoted: the sly intermixture of philosophy and theology of Emerson's work on nature, on top of his mastery of the English language: "If the stars should appear on night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God which had been shown!" (493) may not be poetry in prose, but it is something quite close, and furthermore, it manages to convey a feeling of nature's grandeur while still keeping the words simple and to the point.
Moreover, Emerson demonstrates his grasp of language not just by his writing style, but also by his control over "Nature" and its' subject, of human society comparing to the natural order and coming up short. Unlike the Old Testament prophets to whom he is alluding since the first sentences of his "Introduction", Emerson does not tell his readers directly that the human society is petty and flawed and that we still do not know from where we did come from despite all of our scientific temporal knowledge, but he still manages to convey that feeling indirectly, even in the "Introduction" and the first chapter, "Nature", where he is still reserved and inhibited, as opposed to the later chapters, where he spares no pains to demonstrate how all of "uses" in the "clause of the world" (495) are second-rate as compared to their counterparts in nature.
Finally, these passages are important because they introduce the rest of the essay in a way that is reserved yet clearly subtle enough to clarify what "Nature" will be talking about in its' main body - not an easy feat for a relatively short introduction of such a long essay.
Therefore, let us conclude the essay with summarization of the importance and creativity of the passages on pages 492 and 493: though they do not appear particularly important to the essay's main message, they do reveal the message of Emerson's "Nature", his mastery over both the written word and the writing style, and they do what introductory paragraphs of an essay must do: introduce the subject of the essay without dwelling on it too much or for too long, like the main paragraphs do. Moreover, this is the reason why the passages on pages 492 and 493 are important.