Here's what we know about our speaker: the dude (and we just have to assume it's a he, since we have no evidence to the contrary) is a poet from Paumanok. As well, he has some very Transcendental ideas and a serious case of wanderlust.
Hmm—does this sound like any (famous, travel-loving Transcendental) poet who often wrote about Paumanok) that you might know?
Okay, so let's pretend that we don't automatically assume that the speaker of the poem is Whitman. After all, it's never a good idea to mix up your poets with your speakers, just in case they're written through a character's point of view. So, what else do we know about our speaker in this case?
Well, he's having a deep existential crisis, at least for part of the poem. His successes in poetry all seem silly, and he feels like he has no idea who he is or how the world works.
He also feels a deep affinity with nature. Ultimately, he decides that nature is everything around him, including himself. This sense of unity changes his tone; our poem goes from bleak to hopeful (while retaining those same Transcendental ideas and sense of wanderlust that Whitman is known for, of course).
All in all, it seems like our speaker is searching for meaning, for connection in this poem. The good news? Well, he finds it. By the time everything wraps up, he seems himself as part of a vast and connected web of energy, one that includes him, the oceans, and all the little bits on the sand. Crisis: over, and it's all thanks to a walk on the beach.