What is Whitman's understanding of the "self" in Section 1 of "Song of Myself"?

I think one prominent truth that is established in section
one (and carried out throughout the rest of the poem) concerning Whitman's view of
"self" is that although he is speaking about himself (this is
definitely an autobiographical/philosophical poem), he does not speak for himself
alone. This part is made obvious in the last line of the first
stanza:

And
what I assume you shall assume,
For every atom belonging to me as good belongs
to you.

Besides the evidence
that "self" is supposed to be a collective word, in this first section, Whitman next
establishes a tone of appreciation for life - the fact that he did not come from nothing
and thankful for the things that he is made up of.  In this way "self" is not
selfish but rather, a grateful self that knows where it came
from.

Finally, Whitman establishes a very obvious tone that
death is inevitable.

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I, now thirty-seven years old in perfect health
begin,
Hoping to cease not till
death.

The majority of the
rest of "Song of Myself" revolves around this idea - the inevitability of death as a
reason for appreciating life.  By using the idea of "self" - Whitman shows how he
considers all men (mankind) to be connected through the element of death, and as a
result, we should all be thankful for life - and live it to the
fullest.