Macbeth first meets them after the battle against the Norway and they predict that he will be Thane of Cawdor and then King. At first he can not believe this but when he finds out he is Thane of Cawdor he and Banquo are surprised. Banquo says, 'Can the devil speak true?' in surprise. This shows us they did not expect the witches to be telling the truth. After this Macbeth seems to be astonished and Banquo points out 'Look how our partner's rapt', which shows us Macbeth is deep in thought about the third prophecy. Therefore, we could argue that the witches make him feel that he will be king and that it is his destiny. He is always thinking about the prophecies after this and drops hints to Banquo, for example he says, 'Let us speak our free hearts to each other'. He is trying to see whether Banquo would be interested in helping him. It also shows his great interest and desire for the throne.
However, we could argue that the witches put real ideas to him that are already in his head. He has great ambition and may already want to be king so the witches therefore could not be totally responsible and just act as a catalyst. We can see it is quite easy to resist the witches as demonstrated by Banquo. He knows the witches could just be trying to plant ideas in his head as he says,
'And oftentimes, to win us to our harm, the instruments of darkness tell us truths, win us with honest trifles, to betray's in deepest consequence'
This saying that often, to bring about our damnation, the agents of evil tell us simple truths, so that we trust them. Then they deceive us in important matters. This shows us Banquo can...