Earl Wasserman contextualizes line 103 in Epipsychidion into Shelley's anti-dualistic philosophy, arguing that Shelley refuses to make a distinction between transcendence and immanence: "Transcendence and immanence, then, can be relatively indifferent alternatives; or, indeed, they can be combined when the transcendent is conceived of as visiting a self, however inconstantly. Therefore the Emily of Epipsychidion only radiates a light that enfolds her but is at the same time wrapped in Beauty 'which penetrates and fills the world' [...]; and in Prometheus Unbound the renovated Earth is folded not only in the light radiated by its own joy but also in 'heaven's smile divine' [...] (186).
The quote from Prometheus Unbound can be found in line Act 4, line 439. Let's look at its surrounding lines to see how it may be "wrapped up" in the idea that immanence and transcendence can be combined.
THE EARTH
As the dissolving warmth of dawn may fold
A half unfrozen dew-globe, green, and gold,
And crystalline, till it becomes a winged mist,
And wanders up the vault of the blue day,
Outlives the noon, and on the sun's last ray
Hangs o'er the sea, a fleece of fire and amethyst.
THE MOON
Thou art folded, thou art lying
In the light which is undying
Of thine own joy, and heaven's smile divine;
All suns and constellations shower
On thee a light, a life, a power,
Which doth array thy sphere; thou pourest thine
On mine, on mine! (431-42)
The earth and its contents are "folded" in a "light which is undying." Thus, the Platonic ideal seems to be collapsing in this passage. The world is a part of the permanence, dependent, sure, on the light of heavenly bodies such as the moon and sun, but the very presence of the Earth justifies the existence of other heavenly bodies. The eternal "soul" is dependent on its immanent contents. Consider another passage from Wasserman:
What Shelley sought by constructing his intellectual system and by refuting the dualism of thought and matter was to liberate the mind from false restrictions and thereby to expand the bounds of reality. If we define "life" as "that which we are" and the "world" as that which we "feel," then "Life and the world...is an astonishing thing," a singular, indivisible entity; and actually our existence and our feelings, or ourselves and what we call the "world," Shelley wrote in a sentence that could have been by Coleridge or Schelling, are subsumed in "Life," which "includes all." Only through the deception of habit, Shelley argues, only through [..] feelings and reasonings that are "the result of a multitude of entangled thoughts, of a series of what are called impressions, plated by reiteration' [...] are we led to the illusion of a distinction between ourselves and the world that exists by virtue of our consciousness of it: "in living we lose the apprehension of life." this is why he can maintain that any 'popular dogma' about reality is inevitably false, since it arises from minds that misunderstood their own nature, having been misled by the repletion of the same "thoughts," as Berkeley and Hume so argue, to suppose those "thoughts" are independent of the mind. (141-42)
This passage reminds me of John Dewey's "art as experience" theory, which he argues is anti-Platonic in that it refutes the notion that art can be separated from "its conditions of origin" (Art as Experience 3). In the following passage, Dewey criticizes the notion that "sense" is an opiate that obfuscates truth:
The desire to derogate from immediate sense-qualities--and all qualities are mediated through some mode of sense--is reinforced by fear of sense, moralistic in origin. Sense seems, as to Plato, to be a seduction that leads man away from the spiritual. It is tolerated only as a vehicle through which man may be brought to an intuition of immaterial and non-sensuous essence. In view of the fact that the work of art is the impregnation of sensuous material with imaginative values, I know of no way to criticize the theory save to say that it is a ghostly metaphysics irrelevant to actual esthetic experience. (293)
Dewey's project seems to be similar to Shelley's: both want to legitimate aesthetic experience as worth cherishing and not in need of contextualization. The very contextualization of aesthetic experience, in fact, reduces the experience to a subordinate, impotent status. When Shelley says poets are "the legislators of the world" in Defence of Poetry, he is arguing for an existential truth, that reality is can be changed by the creative energies of the poet.
Wasserman, Earl. Shelley: A Critical Reading. Baltimore, Johns Hopkins P, 1971.