Although the Porter is rather drunk, the jokes that he makes about keeping Hell's Gate become reality when Macduff discovers the terrible scene in the King's bedroom.
He describes himself as the "devil-porter" letting people into "hell". He is really Macbeth's porter letting people into Macbeth's castle and he is calling the castle a type of hell on Earth. This is a good example of dramatic irony as the reader knows what has been going on in the previous scene. Shakespeare uses a lot of dramatic irony in this particular scene.
This scene is also one of my favourite scenes as the language is a bit easier to understand and is different to the language in the other scenes. Shakespeare uses sentences such as, "Here's a knocking indeed", "If a man were porter of hell-gate" and "turning the key". It is sometimes rather tedious reading a piece of text and not understanding all of it.
Another reason I like the language is that the words Shakespeare uses words related to hell to give the scene a lot more effect. He uses words such as "equivocator", nouns such as "Beelzebub" and phrases such as "have napkins enow about you, here you'll sweat".
The Porter is also one of my favourite characters as he is humorous and it is good to have a funny scene in the midst of all the tragedy of this play.
Later on when Macbeth and Lennox are talking, we get the picture that Macbeth is upset and feels guilty for the deed he has committed because he says: "`Twas a rough night."