Analysis for "two truths are told... but what is not" speech

Macbeth's speech (Act 1, scene 3, lines 128-142) is very important to the play's plot. This is because of three reasons. Firstly, the first truth is told from the witches' prophecies. Secondly, this extract shows Macbeth's reaction to the first prophecy coming true in his thoughts. Lastly, his speech shows the start of Macbeth's vaulting ambition. The three witches revealed to Macbeth that he will soon become the Thane of Cawdor, and later onwards, the King. You …

…then his conscience kicks in and tells him that he is too scared of doing so. However, his ambition steps forward and finishes Macbeth's speech with "nothing is but what is not". Hence, this extract is very important to the rest of the play because the first of the two prophecies become true and thus this unfolds the plot, you are told of Macbeth's reaction to this coming true and finally, the ambitious Macbeth begins.