In this section, Whitman expresses a unity and comraderie with everyone else on the planet; he feels connected to them, at one with them, and as much a part of them as they are of him. He expresses an attitude of congeniality, of acceptance, of wholeness, of satisfaction and of confidence in his belief that we are all connected together on this earth. Not one of us is an island, standing alone with no connections to other people. As he says in the section,
"These are really the thoughts of all men in all ages and lands, they are not orignal with me. If they are not yours as much as mine they are nothing."
These first few lines express how Whitman feels even about his thoughts that he has been writing in his poetry--he does not claim exclusive ownership of his poetry or thoughts. He believes that his thoughts are only ones that we all have pondered at one point or another; they belong to everyone; everyone shares these same sentiments, and he is just the voice that is putting them down on paper. His attitude of connectedness and unity with the rest of humankind is expressed not only in this section, but in many other sections of the poem also. I hope that those thoughts helped; good luck!