Answer
The porter in Act 2, Scene 3 is an example of comic relief because he provides a humorous break from the intense action of the play. He delivers a few humorous lines, such as "Faith, here's an equivocator, that could swear in both the scales against either scale; who committed treason enough for God's sake, yet could not equivocate to heaven" and "Marry, here's grace and a cod-piece; that's a wise man and a fool".