Quote 25
MACBETH
Hang out our banners on the outward walls.
The cry is still "They come!" Our castle's strength
Will laugh a siege to scorn. Here let them lie
Till famine and the ague eat them up.
Were they not forced with those that should be
ours,
We might have met them dareful, beard to beard,
And beat them backward home. (5.5.1-8)
Macbeth's strategy during the siege is to hole up in the palace and bide his time "till famine and the augues" (starvation and illness) destroy the enemy soldiers. What's creepy about this is that he's still acting like he has all the time in the world, when in fact his borrowed time is just about up. (Fun fact: plays are bound by time in the way that other works of literature aren't. You can read a novel as fast or as slowly as you want, but when you're watching a play you only get the amount of time that a director has assigned. Almost—we're just saying—as though you're being controlled by fate.)
Quote 26
MACBETH
She should have died hereafter.
There would have been a time for such a word.
Tomorrow and tomorrow and tomorrow
Creeps in this petty pace from day to day
To the last syllable of recorded time
And all our yesterdays have lighted fools
The way to dusty death. (5.5.20-26)
You can interpret this speech six ways to Sunday, but it seems pretty clear that, however he feels about his wife, Macbeth is pretty sure that he no longer has a future.