In Macbeth's soliloquy in act III, scene I, lines 48-72, he reviews his problems of a fruitless crown. Influenced by the witch's prophecy, Macbeth decides Banquo is a threat to his thrown. In this soliloquy one can see much of Macbeth's characteristics, as seen also in others throughout the play.
With Banquo as a threat to the throne, Macbeth questions his own presence in his present spot. He asks why he is put there if there is no one to follow in his footsteps from his own bloodline. At the end of the soliloquy he decides to take fate into his own hands. With these thoughts being revealed, Macbeth's character starts to become more evident. This also reveals characteristics that are not seen until his throne is threatened. The main flaw that one can see in Macbeth's character is one that much of society has today.
His instinctive reaction to protect his throne by any means necessary is related to man's instinct to protect his property. This proves to be a necessary characteristic to survive in today's world; however, Macbeth's inability to control the extent of his instincts shows how lack of self-control can affect one's life greatly. This single trait affects Macbeth for the rest of the play and causes him to do rash things without understanding the consequences.
Lack of self-control and instinctive reactions are Macbeth's most distinct characteristics; however, in Shakespeare's tragedy his character is so well rounded that one can see all of these traits in just one soliloquy. With this in mind, almost everyone who reads this tragedy can relate to Macbeth at least once in the play. This is what makes his soliloquies so important to the plot. One can conclude that without these additions the play would not have the same effect.