Whitman is taking on different personalities. He's a shape-shifter who can assume the identities of other people at will.
He takes on the identity of a hunter in the mountains.
He wanders through the forest and stops for the night to sleep and eat the game he has killed.
He becomes the captain of a ship called a "Yankee clipper" and eats chowder with other sailor-types.
Poof! Now's he's in the West to see the marriage of a beaver trapper and a Native American ("red") girl. He describes the richly dressed trapper and the healthy young girl.
Now he plays the role of a man who shelters a runaway slave. Whitman, who wrote this poem a few years before the Civil War broke out, was firmly against slavery.
He treats the wounds of the former slave and gives him food and shelter. He invites the slave to dine at his table and, tellingly, has no fear that the slave will ever try to take his rifle ("firelock").
Whitman has a seemingly limitless trust in other people.