In Act V, scene v, of Macbeth, what is the main idea of Macbeth's soliloquy after hearing his wife has died?

In Shakespeare's Macbeth, Macbeth
delivers his famous "Tomorrow, and tomorrow" speech in Act V, following his wife's
suicide.

When the reader first sees Macbeth and Lady
Macbeth together for the first time in Act I, though she is harsh and overbearing, they
share sentiments that speak of a genuine affection for one another. Ironically, where
Macbeth is squeamish about murdering Duncan, and Lady Macbeth has no qualms at all, as
the story progresses, the blood they shed weighs heavily on Lady Macbeth's heart and
mind, while Macbeth embraces the tyrant's role, murdering more often, and seemingly,
with more ease.

By the time the end of the play nears, Lady
Macbeth has gone mad, walking in her sleep, and repeating conversations that prove the
she and Macbeth were complicit in a long list of murders. Macbeth still is concerned for
his wife, asking the Doctor to do something for her.

When
Macbeth learns of his wife's suicide, it is important to remember that he is growing
tired of the killing and the disappointment of wanting something (the throne) and
finding little joy in the having of it. His thanes are not only deserting him, but are
joining the other side to fight against him. In Act V, scene iii, Macbeth bemoans the
fact that he is tired of his life:

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I have lived long enough.  
(22)

He notes that as he
ages, so much more quickly now it seems, that he has no group of friends to keep him
company, no honor or love—

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...but in their
stead,

Curses, not loud but deep, mouth honor,
breath,

Which the poor heart would fain deny, and dare not.
 (26-28)

By the time he hears
of Lady Macbeth's death, Macbeth has begun to lose faith. He looks at life as a
collection of meaningless actions:

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And all our yesterdays have lighted
fools

The way to dusty death.  
(22-23)

In other words,
everyone ends up in the same situation: dead.

The famous
line, "Out, out, brief candle!", refers to the brevity of life. He describes each person
as one who, like a player on the stage, acts and speaks his lines, but it is all
meaningless in the end, and forgotten.

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It is a tale

Told by
an idiot, full of sound and fury

Signifying nothing.  
(26-28)

Perhaps we can assume
that after all that Macbeth has done to gain the throne and keep it, he finds it of
little value, not worth sacrificing his immortal soul. (He murdered a King, a sin
against God.) It would appear that being King no longer brings him
pleasure.

Macbeth realizes that life is short, and facing
his mortality, it seems that he finds that all he has done, in the end—in the face of
certain death—is unimportant. Had there been any doubt in his mind before, Lady
Macbeth's death leaves him completely alone in the world.