We witness Macbeth's first reaction to the witches' prophecy through the words of Banquo, who is with him:
Good sir, why do you start and seem to fear things that do sound so fair?
Banquo can't help but notice that Macbeth seems startled, fearful, and riveted by their words. Macbeth overreacts to the prophecy, leading to Banquo's question and comment that the news seems "fair" or good to him, so why such fear? Banquo doesn't know that Macbeth reacts this way because the witches are stating out loud Macbeth's deepest, most forbidden desire to be king of Scotland.
After his stunned reaction, Macbeth's first words to the witches are as follows:
Stay, you imperfect speakers, tell me more.
By Sinel’s death I know I am thane of Glamis.
But how of Cawdor? The thane of Cawdor lives,
A prosperous gentleman, and to be king
Stands not within the prospect of belief,
No more than to be Cawdor.
Macbeth wants the witches to stay longer and to tell him more about where they have gotten the ideas, which seem incredible to him, that he could become thane of Cawdor or king of Scotland. This is a moment of dramatic irony
, in which the audience knows what the characters in a play do not. We know from the last scene that the traitorous thane of Cawdor, who sided with the Norwegians against Duncan
, has been put to death. Duncan has already announced he is giving the title of thane of Cawdor to Macbeth to reward him for his valor on the battlefield. Macbeth and Banquo have no idea, however, that any of this has occurred.
The witches will not be commanded by Macbeth. They disappear without any explanation.