In Act 3, Scene 4 of Macbeth, what is the dramatic significance?
In Macbeth, Scene 4 of Act III is significant to the drama because it is the first time in the play that Macbeth voices his inner conflicts in public; this revelation of his fears to others marks a turning point in the play. For, events at the banquet show that Macbeth can no longer pretend to be innocent.
Despite Lady Macbeth's attempts to explain to the guests that Macbeth's "fit is momentary" (III,iv,67), the guests are bewildered as Macbeth talks to the ghost of Banquo, challenging it, even. Lady Macbeth has lost control of her husband, so she asks them to leave lest they hear him confess his murder of Duncan.
In addition to the revelation of Macbeth's fears, there is much mention of blood by Macbeth as well as the supernatural:
It [the ghost] will have blood, they say: blood will have blood./Sones have been known to move and trees to speak;/Augures and unerstood relations have/By maggo-pies and choughs and rooks brought forth/Te secret'st man of blood. What is the night?
Macbeth feels himself mired in blood, murder, and at the mercy of the supernatural with the omens that he senses. In short, he is very conflicted and disturbed. This disturbance within Macbeth and the references to blood foreshadow both his bloody end and the breakdown of Lady Macbeth, as well.
The ghost of Banquo is, reflectively the hallucination issued from Macbeth's troubled mind. This thought makes him think of the other probable sources of danger. Wishing to allay such fears, he decides to meet the weird sisters to know what is in store for him. But more worrying is his determination to set aside all considerations of prudence and conscience in order to seek his selfish ends.