Early on in Emerson's essay, he uses a metaphor alluding to a scientist named Boscovich, whose ideas were foundational to atomic theory:
Was it Boscovich who found out that bodies never come in contact? Well, souls never touch their objects.
Emerson is referring to the idea within atomic theory that matter is composed of tiny particles that, in their most basic form, never actually come into contact with one another. Rather, the particles are drawn so close to one another that we can no longer perceive the negative space between them. Emerson uses this concept from physics as a metaphor for his philosophical theory of subjective experience. Individuals may be able to form bonds with one another, such as the bond Emerson had with his son while he was alive. Nevertheless, even two bonded individuals can never permeate one another's spheres of existence. We are always locked in our own subjectivity and can merely brush the surface of another person's reality.
Emerson's idea of physics is not absolutely correct, but his choice of metaphor is significant. Philosophy and physics are, at their highest level, interrelated because they each attempt to describe how the world works. Emerson's work is deeply rooted in his personal experience, and he does not believe that empirical observation (the cornerstone of most branches of science) captures all the truth about life. By drawing on the world of physics, which does support the notion of truths we cannot observe, Emerson positions his work as not antithetical to serious science but rather scientific in its own right.
After describing many religions' imperfect attempts to get at the way human life represents something greater we are always trying to touch, Emerson turns to a frustrating problem with philosophy. He alludes to the Fall of Man in the Bible and also to Plato's Republic:
It is very unhappy, but too late to be helped, the discovery we have made, that we exist. That discovery is called the Fall of Man. [...] We have learned that we do not see directly, but mediately, and that we have no means of correcting these colored and distorting lenses which we are, or of computing the amount of their errors. Perhaps these subject-lenses have a creative power; perhaps there are no objects. [...] Nature and literature are subjective phenomena; every evil and every good thing is a shadow which we cast.
In the Bible, Adam and Eve are punished with mortality for disobeying God by eating fruit from the Tree of Knowledge. They become self-aware and are cursed to live their lives striving for reentry to the paradise of Eden. Emerson thinks of philosophy as the same sort of process: he and other philosophers know that there is something greater than human life, and they are always trying to get a glimpse at it. Philosophers too are cursed because there is no way to "[correct] these colored and distorting lenses" of subjectivity, and there is no way to know how much they are skewing our view of objective reality. Emerson goes so far as to say that there may be no such thing as "objects." That is, the world may exist solely in our perception of it, and we will never know. Even if this is so, there is still a greater "objective" reality which is the sum of all subjective experience. No one will ever have access to that reality.
Emerson's declaration that "every evil and every good thing is a shadow which we cast" seems to be an allusion to Plato's allegory of the cave. In Plato's Republic, a book that was highly influential to Emerson, the ancient philosopher describes a cave in which prisoners are kept facing a wall, onto which puppeteers project the shadows of various objects, like books. The prisoners see the shadows and name them as if they are the real objects, but really they are naming mere shadows of real things. If the prisoners turn their heads, they can realize the difference. For Emerson, the frustrating experience of being a philosopher is that he knows he is only ever seeing "shadows" of true evil and good, projected through the lens of his experience. At the same time, if he turns his head, there is still no way for him to see anything other than these same "shadows."
