Commenting on lines 303-20, Earl Schulze compares the cave to Dante's purgatory. According to Schulze, the cave "does not heal his self-division. It lays him open to unimaginable terrors that words themselves can only conceal. Yet, clearly, this is the level of internalization that the quest has required from the beginning, and perhaps significantly, it is reached through a relaxation of consciousness and will" (210).
Schulze, Earl. "The Dantean Quest of Epipsychidion." Studies in Romanticism. 21.2 (2002): 191-216.