What is Macbeth's state of mind before and after killing Duncan
After Macbeth receives his prophecy from the Three Witches, he becomes enamored with the idea of one day becoming king. He recognizes his ambitious nature and feels terrible about his thoughts of committing regicide. After contemplating the consequences of murdering King Duncan, Macbeth decides against his ambitious nature and chooses to not kill the king. Macbeth's mental state before murdering King Duncan could be described as anxious and somewhat confused. Macbeth understands that he wants to become king, but he is initially unwilling to murder King Duncan to take the title. Unfortunately, Lady Macbeth persuades her husband into committing regicide.
Following Duncan's murder, Macbeth becomes overwhelmed with guilt and anxiety. Macbeth immediately begins to experience auditory hallucinations following the murder and has difficulty concealing his emotions. In order to secure his throne, Macbeth orders the murders of Banquo and Fleance, as well as Macduff's entire family. Macbeth begins to lose sleep and even sees Banquo's ghost during a banquet feast. Macbeth gradually becomes a tyrant as his mental state declines. He becomes a bloodthirsty, unsympathetic ruler, who is overconfident in his abilities to retain his title as king. By the end of the play, Macbeth is an isolated, defeated tyrant, who cannot defend his throne. Macbeth accepts his unfortunate fate and dies at the hands of Macduff.
In the play 'Macbeth' by William Shakespeare, Lady Macbeth and the witches have wound her husband up into a frenzy of ambition and desire for power. Before killing Duncan, he is more motivated by these desires than by a desire to kill or murder for it's own sake. He has nothing against Duncan other than that he stands in his way of getting those things. By the time he is ready to do the dirty deed and actually kill Duncan, he has retreated into himself and become obsessed with one idea alone. We call this becoming fixated. His fixedness pushes everything else away. He pushes every thing and every one else out - including his wife Lady macbeth. He has become unreachable by reason or moral thought and his relationship with his wife has changed - they are no longer a couple - and he takes over the momentum alone.
Before Macbeth kills Duncan, the king, he is nervous and already feels guilty. You can best see this in the part (in Act II, Scene 1) where he has the vision of the bloody dagger. This clearly shows that he is uncertain about what he is about to do.
After he actually kills Duncan (Act II, Scene 2), he feels even more guilty. He believes that he has heard people accusing him of murder. He also finds that he cannot speak the word "amen" when he tries to pray. Both of these show the depth of his guilt.