Here, at about the midpoint of the poem, he declares his manifesto, and we're finally justified in calling our speaker "Walt Whitman."
He describes himself first and foremost as an American, then as a "rough," someone who isn't refined or polished.
Finally, he uses the Greek word "kosmos," which we now use to describe outer space ("cosmos") but which more appropriately means the entire world, known and unknown.
He takes pride in his sensuality and loves to eat, drink, and "breed." (In point of fact, the real Whitman never had any children, so don't forget that the speaker isn't the same as the poet, even if they have the same name.)
One of the poem's most famous and humorous couplets is, "Unscrew the locks from the doors! Unscrew the doors themselves from their jambs!" These lines express Whitman's radicalism, and they are used as an epigram at the beginning of Allen Ginsberg's collection Howl. They are humorous because Whitman initially decides the best way to get through this metaphorical door is to unlock it (sounds reasonable), but then he says, oh, what the heck, and tears the entire door from its frame!
He reaffirms his faith in the principles of true democracy and says that he is a vessel for all different kinds of voices, even "forbidden voices."
Whitman gives voice to people whose voices are not usually heard in society.
In this section he shows his "rough" nature with frank talk about sexuality and the body. He says that "copulation" (sex) is not "rank" or disgusting to him.
He loves the body and even the smell of armpits.
He says that he will worship his own body, his beard, blood, sweat, breast, and semen.
Then he treats nature like a body and worships it, too. He memorably compares the wind to "soft-tickling genitals."
Um. In case you didn't notice, Whitman's description of nature is intensely erotic.
Again he says that one can learn more from nature than books.
Nature makes him humble and aware that he is not a "master" of the world.