In this complicated section, Whitman begins by naming some of the mysteries of life. He has a suspicious tone ("Who goes there!"), as if someone uninvited had just shown up to his party.
(But, hey, wasn't everyone invited to the party?)
His point in this section is to address the skeptics and cynics who say that "life is a suck and a sell." That is, life's just a nasty game played on people.
He could be thinking of Macbeth's famous speech that life is just "sound and fury signifying nothing." Whitman could not disagree more.
He talks about his non-conformity. He does things just the way he likes.
He also addresses the worry that existence might end with death. He doesn't think there is any such thing as "dissolution," because the world is so well built. He's not concerned about what happens after death.