"On the Sea" begins mysteriously. Without the title there to guide them, readers might not even know that the speaker is describing the sea: the speaker merely introduces an enigmatic "it" that whispers around the "shores" of lonely, faraway lands.
The personification here suggests that this "it" could be a spirit, or even an immortal god: its "whisperings" are "eternal," and it can travel to "desolate" places that no human foot has ever touched.
In other words: this poem sees the ocean as more than just a bunch of water. To this speaker, the sea is a conscious, living force. And it seems to have a message to communicate. Those "eternal whisperings" might contain secret wisdom.
The speaker wants readers to hear the ocean's whisper for themselves. Listen to the strong sibilance of these first words:
It keeps eternal whisperings around
Those repeated /s/ sounds—along with the consonant /sh/ and /z/ sounds—are onomatopoeic, sounding just like what they're describing: the steady, quiet hiss of ocean waves.
Right from the start, then, this poem immerses readers in the physical experience of being by the ocean and listening to the surf. But it also invites readers to see this as more than just a physical experience. To hear the "whisperings" of the ocean, the speaker suggests, is to come into contact with some mysterious spirit of nature. The rest of this poem will explore this sea-spirit's personality and encourage readers to get to know it for themselves.