William S. Davis claims the poet's Ionian isle "is a realm in which we find a natural harmony between the human subject and all material objects ('a soul within the soul')--a harmony that depends, not on any artificial arrangements, but on an affinity that points to a relation prior to mortal life" (63). Davis's comment is based on line 456 of the poem. One of Davis's principle objectives in his essay is to suggest that Shelley viewed the poetic soul as picturesque in nature. Davis's commentary on lines 481-82 speaks addresses this issue.
Davis, William S. "Living Landscapes: Schelling, Goethe, Shelley." 2002. 49-71.