What is Macbeth's state of mind before killing Duncan?

           Macbeth, after discussing the crime with Lady Macbeth, has decided to go through with the "terrible feat". Now he sits alone, waiting for the bell which will summon him to murder Duncan and pondering his decision one final time. He is nervous and already feels guilty. We can see this in the part when he has the vision of the bloody dagger floating in air. This clearly shows that he is uncertain about what he is about to do.

           But Lady Macbeth and the witches have already wound Macbeth up into a frenzy of ambition and desire for power. So before killing Duncan, he is more motivated by these desires than his conflicts in mind. By the time he is ready to do the dirty deed and ultimately kills Duncan.

            The soliloquy of Macbeth relating to the scene of the invisible dagger, is our first glimpse of Macbeth's powerful imagination which is largely responsible for his mental torment throughout the drama.