The poem is overflowing with rich, vivid imagery that evokes the beauty of the shore near the Italian city of Naples. The speaker's detailed descriptions reveal just how closely he's observing the natural world, making his sense of separation from it all the more poignant.
The speaker also often personifies nature within this imagery, making the world around him seem distinctly alive: the waves are "dancing fast and bright," while the "Blue isles and snowy mountains wear / The purple noon's transparent might." The rich colors here—"blue," "snowy" white, and "purple"—suggest the vividness of the landscape while also subtly hinting at the speaker's dejected spirits, which seem to cast the world in somber tones.
The imagery here isn't just visual: the speaker also notes the sounds of the wind on the water, of the birds flying overhead, of waves on the shoreline, and even of the city in the distance. These sounds all seem to swirl together, different notes belonging to a singular "voice of one delight." This imagery, in turn, highlights the speaker's isolation: the voice he doesn't mention here is his own, implying that he isn't a part of all this lovely harmony.
Likewise, in the second stanza, the speaker juxtaposes intense imagery of the ocean—from the darkness of its deepest depths to the way sunlight bounces of its surface—with his own position sitting "upon the sands alone." Even as the speaker highlights his separation from the beauty around him, however, he still manages to convey the serene, peaceful beauty of the scene at hand, with the "measured motion" of the waves.