How is Book 13 essential to both the structure of the narrative and in the progression of the narrative's many conflicts?

This episode marks a change in the Greek attitude toward hospitality. While the Phaeacians are gracious as ever in helping Odysseus, the fulfillment of the prophecy and sinking of their ship forces them to stop helping travelers. Zeus wearily permits the destruction of the ship only because Poseidon feels he has been wronged by the other gods; ensuring harmony among the gods, it seems, is more important than maintaining hospitality at all costs among the mortals.