comment on the Dagger scene.

I think the translation says it best;

“Is This A Dagger Which I See Before Me” Soliloquy Translation:

It was totally silent. And pitch black. It was now or never. Macbeth stared into the darkness. And as he looked it seemed that a dagger hung there. He closed his eyes and opened them again. It was still there. He peered. It didn’t waver. Was it really a dagger? Its handle towards his hand?

He tried to clutch it. His hand went right through it: it was still there and yet he couldn’t feel it. Was it only a dagger of the mind, a false creation of a fevered brain?

He could still see it as he drew his own, real, dagger: it was pointing the way to Duncan’s room. He knew he was seeing things and yet it was so real. And now there was blood on it, which hadn’t been there before.

It was ridiculous. There was no such thing. He knew it was the violence in his mind that was coming out in the form of a bloody dagger.

His mind was filled with images of fear and horror and he stood there, overwhelmed by them, until a bell rang and brought him back to the business in hand.

‘I go, and it is done: the bell invites me.’ He began walking. ‘Don’t hear it, Duncan; for it’s a knell that summons you to heaven or to hell.’

Macbeth’s trepidation about the murder is echoed by several portentous sounds and visions, the famous hallucinatory dagger being the most striking. The dagger is the first in a series of guilt-inspired hallucinations that Macbeth and his wife experience. The murder is also marked by the ringing of the bell and the knocking at the gate, both of which have fascinated audiences. The knocking occurs four times with a sort of ritualistic regularity. It conveys the heavy sense of the inevitable, as if the gates must eventually open to admit doom. The knocking seems particularly ironic after we realize that Macduff, who kills Macbeth at the end of the play, is its source. Macbeth’s eventual death does indeed stand embodied at the gate.

The motif of blood, established in the accounts of Macbeth’s and Banquo’s battlefield exploits, recurs here in Macbeth’s anguished sense that there is blood on his hands that cannot be washed clean. For now, Lady Macbeth remains the voice of calculating reason, as she tells him that the blood can be washed away with a little water. But, as Lady Macbeth eventually realizes, the guilt that the blood symbolizes needs more than water to be cleansed away. Her hallucinations later in the play, in which she washes her hands obsessively, lend irony to her insistence here that “[a] little water clears us of this deed” (2.2.65).