Shakespeare was well aware of the significance of juxtaposing comedy with tragedy. For, not only did it provide relief from the seriousness of the play, but it also left the laughing audience somewhat disarmed and more vulnerable for the shock of a subsequent tragic event. In addition, Shakespeare employs the colloquially speaking porter as a break from the verse, which will make the audience listen intently, to inform about the theme and the forthcoming words of Macbeth:
...here's an equivocator that can swear in both the scales against either scale [Macbeth lies about killing the guards to Duncan's chamber]who committed for God's sake, yet could not equivocate to heaven. O come in, equivocator! (2.3.8-11)
The porter also figuratively "opens the door" to the death of Duncan as he says "drink...makes him and mars him," as well as to Macbeth's lying in his words which have a double meaning:
in conclusion, equivocates him in a sleep, and giving him the lie, leaves him. (2.3.31-32)
And, then, for his part of this scene, Macbeth restates what the porter has previously said rather bawdily about lying and about not getting into heaven in a situationally ironic passage as Banquo and Malcolm and Donalbain are not aware of the truth:
Had I but died an hour before this chance,
I had lived a blessed time; for from this intant
There's nothing serious in mortality...
All is but toys. Renown and grace is dead,
The wine of life is drawn, and the mere lees
Is left this vault to brag of. (3.2. 99-104)
The comedy of the porter before the tragic scene provides comic relief as well as suggesting insights into the theme and the character of Macbeth. The prose and comic relief provide a contrast to the rest of the scene, a contrast that causes the audience to listen better and be more moved by the tragic events that follow.
The porter scene shows Shakespeare's skill as a playwright. After the intense scene of the assassination of Duncan, we have the humor of the porter's scene. The comedy of this scene breaks the tension of the previous scene. And yet it is in keeping with the themes of the play. The drunken porter believes he is in hell. This is humorous, yet thematically accurate. In killing Duncan. Macbeth has created a personal hell. Macduff's knocking disturbs the porter, who equates it with various sinners knocking at the gates of hell.
When he finally admits Macduff, the porter goes on to joke about the effects of alcohol. Macduff reacts in amused indifference, much as the audience reacts to the porter's antics. The porter provides a comic break between major dramatic events. What follows the porter's scene is Macduff''s discovery of Duncan's body. Much needed comic relief is supplied through the witticisms of the porter.
This is just to look at the manifold significance of the scene synoptically.
1. It provides a comic relief after the starkest moment of Duncan's murder.
2. It has a theatrical importance. The actors playing Macbeth and Lady Macbeth must get some time to change their blood-smeared clothes to come back on stage and pose innocence.
3. Porter's comparison with devil porter and inverness with inferno heightens the evil nature of Macbeth's deed.
4. The three frame-stories about the farmer, the tailor and the equivocator all spell out the nemesis of vices like ambition and greed. Their narratives echo and reinforce the central tragic narrative of Macbeth.
5. The porter's speech is a welcome relief in prose from the verse style used thus far.
6. It is a choric speech and as always in Shakespeare, it comes from the mouth of a subaltern. In Macbeth, there is another of these choric speeches as spoken by an old man.