This quotation is spoken by Macbeth in act 2, scene 2, of William Shakespeare’s Macbeth. In this scene, Macbeth has murdered King Duncan, and he speaks this soliloquy while Lady Macbeth is placing the daggers that he had used on Duncan’s chamberlains. This speech can be seen as the first time Macbeth realizes the depth of what he has done and that it is not anywhere near over yet. He has murdered in order to gain the title of king, but now he sees he must continue to shed blood in order to keep it.
To best analyze this quote, let’s break it down line by line.
Whence is that knocking?—
This one is self-explanatory—someone has knocked on a door somewhere that Macbeth can hear it.
How is’t with me, when every noise appals me?
Macbeth now asks himself why he was frightened by this noise. Before this instance, Lady Macbeth had been frightened by a hooting owl. Both characters, portrayed as strong and intelligent, are suddenly jumpy and fearful.
What hands are here! Ha, they pluck out mine eyes.
Macbeth now notes his own hands, which are covered in the blood of Duncan. He then laughs, saying they pluck out his eyes. This is most likely in reference to the line he spoke moments beforehand, when he said he could not stand to look upon Duncan’s dead body anymore. The laugh can be considered a sign of Macbeth's mental stability starting to crumble.
Will all great Neptune’s ocean wash this blood
Clean from my hand?
Now Macbeth is wondering if his hands will ever be clean, if the entire ocean would even be enough water to wash with. This is also a parallel to Lady Macbeth, who later becomes obsessed with washing blood off her hands even though they are clean.
No, this my hand will rather
The multitudinous seas incarnadine,
Making the green one red.
Macbeth believes his hands will never be clean. Rather, these hands will make the vast, huge sea turn red because it will be so filled with blood. He will kill so many people that he will take the green waters of Scotland and change them to red.