Macbeth heard the prophecy from three witches. When Macbeth received the prediction that he will become thane of Cawdor and then it actually happens, his character changes from a nobleman to a villain (with the help of Lady Macbeth). His ambition is what leads him to killing Duncan and so when the witches told him that he would become king, he intensified his efforts to kill Duncan so that he would become the king as soon as possible. This desperation can be seen in Act 1, scene 4,

Explanation:

The Thane of Cawdor was the Scottish Nobleman and was the next possible heir to the Duncan’s chairs.He was trying to end Duncan’s rule and become the king. Duncan sent Macbeth and Banquo to execute  him so his son Malcolm could become the true heir of the throne. As the prophecy made by the three  witches was that Macbeth would become “Thane of Cawdor” and ultimately “The King of Scotland” and  for Banquo the prophecy was “A king would come from his kind”. After Macbeth and Banquo executed  The Thane of Cawdor Duncan was really happy by their work and made Macbeth the new “Thane of  Cawdor”. Now Macbeth started to realize he needs to remove the blockade known as Malcolm to  become the “King of Scotland”. Duncan promises a visit to the Macbeth’s mansion and tells him to go  and share this good with his wife Lady Macbeth. So Macbeth go and tell everything to his wife and about  his blockade between the throne and him too.