Whitman would like us to believe that he is cobbled together out of all the various kinds of people that he has listed in the previous sections.
He's the union of opposites: old and young, foolish and wise, mother and father, the average people and the elites, South and North (remember, he wrote this just before the Civil War) – you get the point.
This section makes clear that Whitman (the poet) is painfully aware of all the fault lines of the great cultural battle that threatens to engulf the United States. The danger of civil war is real, and Whitman's poetic persona attempts to stand astride the rift and hold the nation together for dear life. If he can get the reader to identify with him, then maybe he can get the North and South to identify with each other.
He lists various American states and North American regions before turning his attention to other continents, "Africa Europe or Asia."
Whitman always tries to broaden his reach. You'll never hear him say, "I'm like this group, but not like this group."
He loves the diversity of his identity and wouldn't trade it for the world.
At the end of the section, he returns to the idea that nature is fine the way it is, and, foreshadowing a Radiohead song, that "Everything is in its right place."