In the play “Macbeth,” the title character fears his former friend Banquo due to the second part of the witches' prophecy, stating that it is Banquo's heirs, not Macbeth's, who are fated to sit on the Scots throne. Furthermore, Macbeth is concerned about Banquo because Macbeth knows that Banquo is a man of conscience and good character.
Macbeth is unwilling to accept that he has given his soul, which he calls his "eternal jewel," to eternal damnation so that Banquo's family line can enjoy the power Macbeth killed for. The witches make two predictions for Macbeth, both of which come true. After Macbeth becomes king of Scotland, he begins to focus on the later part of the prophecy. The idea that he has murdered Duncan for the benefit of Banquo's sons and grandsons infuriates him. Macbeth dwells on the idea of the "barren scepter" that the witches have placed in his hands. With some prodding from Lady Macbeth, he decides to preserve the future of the throne for his own offspring.
Although they are friends, Banquo’s first loyalty is to Scotland, not to Macbeth. Banquo becomes suspicious that Macbeth has killed King Duncan and if he were to confirm Macbeth's role in Duncan's death, Banquo might expose him, which may lead the other Scots lords to turn on him and seek justice. This thought troubles Macbeth greatly. Since Banquo is the only one who knows about the prophecy, Macbeth acknowledges that Banquo is a genuine threat to him, saying "There is none but he whose being I do fear.” Macbeth's fear and jealousy prompts him to murder his former best friend.