In Hamlet, what does "To be or not to be" mean?

In Hamlet, the "to be or not to be"
is not about suicide.  Hamlet would not be debating suicide here.  He had debated it
earlier, but the Ghost has presented him with purpose now: kill the king and send him to
hell, thereby freeing the Ghost from Purgatory to heaven.  If Hamlet suicides, both he
and the Ghost will go to hell, and, worse, Claudius might go to
heaven.

Rather, the monologue is a meditation on existence
(the interrelated nature and meaning of life, suffering, and death).  According to
existential critic Rheinhardt Grossman in Phenomenology and
Existentialism:

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Two things keep Hamlet from committing a
suicide: fear of death and uncertainty that waits for him after it and the wish to
revenge for his father’s death. Vainness and confusion are two words which can
characterize all his life. Even when he decides to revenge for his father’s death and
kill Claudius he does not use his chance. He got lost in his eternal thoughts about
useless life, sufferings and pain. He is not able to see the world in a new perspective
and cannot get out from the web of fear, darkness and pain which he himself
created.

The
monologue is about activity vs. passivity in response to suffering and a society gone to
pieces: "to be (active) or not to be (active)" or, conversely, "to be (passive) or not
to be (passive)."  Hamlet wonders if he can withstand all of misery that seems inherent
in the human condition.  Is there a point to suffering?  Should he fight against it or
just accept it as inevitable.  Denmark is a prison: is there a point in fighting to
escape it when the world outside its walls might be a prison as well?  To him, the world
is so corrupt, that life seems pointless.  Should he give up
hope?

The soliloquy might also be interpreted in terms of
the after-life.  It's about being damned to hell by committing revenge or not being
damned.  So, "to be (damned) or not to be (damned)."  The problem of sending the Ghost
to heaven and Claudius to hell will cause him to go to hell as well (murderers go
there).

In the end, though, Hamlet resolves his spiritual
crisis by giving this answer in response to his earlier
monologue:

If
it be now, 'tis not to
come, if it be not to
come, it will be now; if it be
not now,
yet it will come. The readiness is all.
Since no man has aught of what he leaves, what is't to leave betimes? Let
be."

Hamlet
has readied himself for activity and for the afterlife in Act V.  He has thus answered
his own earlier questions.