Act 2, sc. 3 of Macbeth is the scene in which Duncan's body is discovered by Macduff. The scene begins with the comic relief of the drunken porter who is awakened from his slumber and imagines who would be at hell's gate knocking. Then the porter and Macduff exchange some bawdy remarks about the effects of excessive alcohol consumption. When Macduff discovers Duncan's lifeless body, there is much confusion and emotional exchanges. Macbeth quickly kills the guards, saying he did so out of anger at them for killing Duncan. Lady Macbeth faints, or pretends to. Malcolm and Donalbain decide that they may be in danger, too, so Malcolm says he will flee to England while Donalbain says he will go to Ireland. Earlier in the scene, approximately lines 58 - 68. Lennox remarks about the "unruly night" where strong winds and other occurrences were unusual. In scene 4, this unusual night is again mentioned in the conversation between the old man and Ross. This harkens to the idea that because Macbeth killed a king and interrupted God's plan, weird and awful events occurred. Also, this scene tells us that currently the blame for Duncan's murder might be put upon his sons and to tell us that Macbeth is the new king.
Act-II, Scene-III (Synopsis):-As there is more knocking,the drunken porter finally opens the door. Macduff and Lenox enter. Macbeth joins them and Macduff goes in to awaken Duncan. He returns with the news of murder; Lenox investigates the scene and says that the guards seem to have committed the murder as stained with blood they stll slept. Macbeth puts on a show of grief and Lady Macbeth faints(suspected pretence). Macbeth kills the King's guards as if out of anger. Malcolm and Donalbain fearing that their lives are at stake, take to their heels, to England and Ireland respectively.
Dramatic Significance:- The drunken porter's queer imagination and humourous description is structurally important because it is an effective preparation for the tense situation that follows. As the murder of the King is pronounced, the terrified Macbeth wishes that had he died a little earlier he would have been a blessed man. That Macbeth kills the guards is counter-factual.
Act-II, Scene-IV (Synopsis):-Outside Macbeth's castle Ross talks with an old man about the natural calamities that have come to pass this night of murder. Macduff comes in and informs Ross that suspicion has fallen on Malcolm and Donalbain, and it seems that the guards did the deed on their instructions. Macbeth has been chosen the King and has gone to champion coronation.
Dramatic Significance:- The description given by Ross about the previous night's horror is a dramatic interpretation in order to intensify the gravity of the situation. The information regarding the portents is theatrical that gives vent to an air of inauspiciousness. The sudden departure of Malcolm and Donalbain proves anything but promising future for Macbeth.