In his soliloquy in act 1, scene 7, as he reconsiders the wisdom of murdering Duncan to gain the throne, Macbeth says,

Bloody instructions which, being taught, return
To plague th’ inventor ...

In saying this, Macbeth acknowledges that if he kills Duncan, he is heading down a guilty path, because the bloodshed won't end but will keep on multiplying. He will be "plagued"—tormented—with having to shed more and more blood. At this point, because he still has a conscience, Macbeth understands that the many deaths that will follow Duncan's will fill him with guilt and anguish.

In act 2, scene 1, on the brink of killing Duncan, Macbeth states,

Mine eyes are made the fools o’ the other senses,
Or else worth all the rest: I see thee still;
And on thy blade and dudgeon the gouts of blood,
Which was not so before.

Macbeth imagines seeing blood on the blade of his dagger, a symbol of the guilt he already feels about what he is about to do.

In act 2, scene 2, Macbeth returns from murdering Duncan, horrified...

(The entire section contains 2 answers and 822 words.)