There's an episode of The Simpsons when Homer tries to get his perpetually sunny neighbor, Ned Flanders, to admit that he doesn't like something – anything. At one point, Homer asks, "What about mosquito bites?" and Ned replies, "Mmm! Love to scratch 'em!"
The speaker of this poem comes second to Ned Flanders in the contest for Most Cheerful Man in the World. He likes – no, loves – everything in the world, "great or small." The only thing that really bothers him is the possibility that there could be something "between us" or between anyone else in the world. It's the 1850s, and maybe he's noticed that the northern and southern regions of the U.S. just can't seem to get along. Whatever the reason, he's determined to tell his readers, and future readers, about how perfectly the world fits together. And, yes, unlike many poetic speakers, this one is very conscious that he is an author speaking to an audience.
The speaker is on the ferry from Manhattan back home to Brooklyn. We don't know why he was in Manhattan, but he calls himself "Manhattanese," as if that were his nationality. He loves the sights and sounds of the big city. He also loves talking to things. It doesn't matter if they can talk back – he'll talk to everything from other passengers to masts and chimneys.
In terms of education, our speaker talks like a normal person, only more excited. He seems to have heard a lot of speeches in his lifetime. In the 19th century, speech-making or "oratory" was both an important skill and a form of entertainment. People would sometimes travel long distances to hear their favorite speakers. At some points, the speaker talks in grand terms about the Soul and eternity, as if he had heard a lot of preachers. But he doesn't seem to be a big fan of religion: the physical world contains all the "ministers" and "novices" he needs. He might fall into the vague category of "spiritual, but not religious" that has become so common in the modern age.
One other thing to know about our speaker – ah! he's right there! – is that he likes sneaking up on people, or at least watching them when they don't expect it. He keeps moving closer and closer to us and hinting cryptically that he's looking at us. But don't be afraid: he's not a stalker, he's just a really hungry guy. He's hungry for things, including people. They give him "sustenance" and keep him high on life. He's like that uncle from back when you were a kid who would reach out to give you huge, massive, painful bear hugs whenever you came within snatching-distance. Be nice to your uncle Walt. He has good intentions. He just wants everyone to be as cheerful as he is.