Throughout William Shakespeare's play "Macbeth," the title character goes against his moralities and betrays his country, his king, and his loyal friend Banquo. Shakespeare uses symbolism, soliloquies, and dramatic irony to get this overlying theme of betrayal.
In the beginning of Macbeth, three witches portray Macbeth's future by telling him he will become Thane of Cawdor, and then King of Scotland. When Macbeth becomes Thane of Cawdor, Macbeth begins to believe the witches are telling the truth. Macbeth tells his wife, Lady Macbeth, about this coincidence which then begins the unwinding trail of events that lead to Macbeth's downfall. .
Macbeth is a trusted soldier, trusted by his army and by his king but Lady Macbeth, as well as the need for power that Macbeth as a human strives for, come together to kill King Duncan, being his first act of betrayal. In Macbeth's soliloquy regarding the dagger in Act 2 Scene 1, the reader understands that Macbeth does feel guilty about his plans to murder King Duncan. He cannot reveal this sense of guilt to Lady Macbeth because she wants him to be brave in his efforts. But the reader learns that Macbeth is not quite as cold and calculating as he appears to other characters.
Because we are able to know Macbeth's thoughts as verbalized in the soliloquies, we understand his dilemma and temptation as he contemplates killing Duncan. We realize that this murder is not easy for him and that he is fully conscious of the fact that this murder is wrong on many levels. But the temptation to be king is so great that it overrides his scruples. Similarly, at the very beginning of Act 3, Banquo's soliloquy states that he fears that Macbeth has done awful deeds to get his position as the King. However, Banquo cannot reveal his doubts to anyone else for fear of what Macbeth may do to him if he were to learn of Banquo's feelings. This develops dramatic irony as we watch Banquo go on to have a civil conversation with Macbeth about the upcoming banquet.