Macbeth shows feelings of guilt even before he kills Duncan. In his soliloquy in Act I, Sc. 7, Macbeth is struggling with his desire to kill the king. “But in these cases We still have judgment here; that we but teach Bloody instructions, which, being taught, return To plague the inventor.” Macbeth worries that killing Duncan will have consequences when he faces judgment after death. “this even-handed justice Commends the ingredients of our poison'd chalice To our own lips” (Act I, Sc. 7). The poison’d chalice refers to the act of killing Duncan. By killing Duncan, Macbeth kills his chance for eternal life in heaven. He knows he is wrong for even thinking about killing his king.
Macbeth goes on to tell himself why he should not kill Duncan. “He’s here in double trust” (Act 1, Sc. 7). Macbeth talks about Duncan being there not only as a king, but as his cousin and his guest. Duncan should be safe under Macbeth’s roof, but Macbeth is contemplating killing him. “…then, as his host, Who should against his murderer shut the door, Not bear the knife myself” (Act I, Sc. 7).
Macbeth is also filled with remorse immediately before killing Duncan. In fact, he is so affected by his feelings that he actually imagines seeing a dagger in the air before him. “I see thee still, And on thy blade and dudgeon gouts of blood, Which was not so before. There's no such thing: It is the bloody business which informs Thus to mine eyes” (Act II, Sc. 1). The bloody dagger he imagines is a symbol of his guilt and foreshadows his coming madness.
In Act 3, Scene 2, Macbeth shows his tormented state of mind in the following passage of dialogue. At this point he is only guilty of murdering Duncan, but he has made definite plans to have Banquo and his son Fleance murdered that night.
But let the frame of things disjoint, both the worlds suffer,
Ere we will eat our meal in fear and sleep
In the affliction of these terrible dreams
That shake us nightly. Better be with the dead,
Whom we, to gain our peace, have sent to peace,
Than on the torture of the mind to lie
In restless ecstasy. Duncan is in his grave;
After life's fitful fever he sleeps well;
Treason has done his worst: nor steel, nor poison,
Malice domestic, foreign levy,nothing,
Can touch him further.
So Macbeth is being troubled by nightmares which are keeping him from getting a good night's sleep. For him it seems better to be dead "Than on the torture of the mind to lie / In restless ecstasy." This seems to mean lying awake because of being tortured by his own mind. His punishment is what the voice predicted when he heard it cry, "Macbeth shall sleep no more." Macbeth also seems to be admitting that he is experiencing fear. The image evoked by the words "eat our meal in fear" is a striking one. He cannot even enjoy his food because of his fear, and perhaps he is afraid that the very food he is eating might be poisoned. He envies Duncan, who is safely dead and can therefore sleep well. Unlike Macbeth, Duncan does not have to worry about such things as steel (i.e., being stabbed to death), poison, malice domestic, or foreign invasion.