On lines 41-42, Stuart Sperry writes:
The phrase "Youth’s vision" begins to mind the visionary maiden of Alastor and the quest for her which is really a process of inner investigation and discovery. The new countermovement is to find its full expression only with the rhapsodic flight of personal recollection of the second section. The point is, however, that the second, inner-directed movement is present from the outset and seeks to assert itself against the primary. For there are two major impulses that govern the work as a whole. One is centrifugal: the effort to externalize Emily, to see her as an influence governing nature and humankind, a power concentrated in the universe of sun, moon, and stars. The other is centripetal: the recognition that Emily and her power are constituents of the self. The first impulse attempts to project her, to discover her in the images and operations of the macrocosm. The second seeks to find her in the microcosm, the interior world of the self. The poem takes its initial momentum from the first impulse; it is, however, a momentum that cannot be maintained and that collapses. As it does so the second impulse begins to emerge and to provide a tension that polarizes the work and governs its development. (161)
Sperry, Stuart M. Shelley's Major Verse: The Narrative and Dramatic Poetry. Cambridge: Harvard UP, 1988.