Macbeth and Banquo hear a prophecy from three witches. They inform Macbeth and Banquo that Macbeth will no longer be king, eventually Banquos sons will become king. Banquo and Macbeth didnt take them seriously.
After being informed by the witches Macbeth sends two people to murder Banquo and his sons. Macbeth doesn't want any chances of losing his opportunity to be king so he makes sure his throne is secure. The killer killed Banquo but his son escaped.
After the killing of Banquo, Macbeth has not been the same. Macbeth began to hear voices and felt the feel of paranoia. He also began to see visuals of Banquos ghost haunting him making him regret what he did.
The Killer Macbeth has sent is now informing him on the fact the job is not finished. Macbeth is upset because his plan slightly failed. Now Macbeth continues on worrying about the possibility of Banquos sons being king.
The three witch inform them that Macbeth will no longer be the king, eventually Banquo's sons will become king. Banquo and Macbeth didn't take them seriously they didn't believe what the witches had to say.