The witches tempt Macbeth by showing him a future where he is king.
All hail, Macbeth! hail to thee, Thane of
All hail, Macbeth, that shalt be King hereafter! (enotes etext p. 13)
Banquo clearly thinks that they are jesting or messing with him at first, but Macbeth is curious.
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,(75)
A prosperous gentleman; and to be King
Stands not within the prospect of belief,
No more than to be Cawdor. (p. 13)
Basically, he wants to know why they are calling him Thane of Cawdor and king. He is ready to dismiss the whole idea until he finds out he actually is the Thane of Cawdor, “The Thane of Cawdor lives. Why do you dress me in borrow'd robes?” (p. 15) Then he gets promoted. Suddenly, the idea does not seem so absurd.
Clearly, Macbeth had to have had some ambition before the witches tempted him. Yet he never would have expected to be named Duncan’s successor if they hadn’t told him he was going to be king. When he finds out he was NOT named next in line to be king, he is angry.
The Prince of Cumberland! That is a step(55)
On which I must fall down, or else o'erleap,
For in my way it lies. (p. 18)
Macbeth does not show his ambition, and he plays the part of a loyal subject and cousin. It is clear that he is already thinking black deeds.
Stars, hide your fires;
Let not light see my black and deep desires:
The eye wink at the hand; yet let that be
Which the eye fears, when it is done, to see. (p. 18)
So the witches do indeed tempt Macbeth, by showing him the title he is about to get and then telling him he will be king, making him wish to be king.
For the full text, see here:
For more on this scene, see here:http://www.enotes.com/macbeth/act-summary-analysis
For more on Macbeth's character: http://www.enotes.com/macbeth/macbeth-character-analysis