In Hamlet, how does the theme of revenge relate to Laertes and Hamlet?
It is important to recognise the way in which Laertes and Hamlet are constantly compared and contrasted throughout the play. Both want to go back and study, though only Laertes is allowed. Both have fathers who are unjustly killed, and both want to revenge themselves against the perpetrators. The difference is that Laertes is yet another character who, compared against Hamlet's endless procrastination, shows Hamlet up and questions his determination to revenge his father. Note what Laertes says when he finds out about his father:
How came he dead? I'll not be juggled with.
To hell, allegiance! Vows to the blackest devil!
Conscience and grace to the profoundest pit!
I dare damnation. To this point I stand,
That both the worlds I give to negligence,
Let come what comes. Only I'll be revenged
Most thoroughly for my father.
This stands directly in contrast with Hamlet, who spends so much of the time thinking about what has happened and engaged in metaphysical philosophical debate rather than the kind of action that Laertes displays. Both characters therefore have reason for revenge, but the difference lies in the way in which Laertes immediately acts to get that revenge whereas Hamlet delays and pontificates endlessly.
I am going to disagree somewhat with the above post. While both have a father killed and have cause to seek revenge, Laertes is no more moved to act than Hamlet is. They both profess their desire for revenge on wings as swift as meditation, but meditation is as far as it gets. Laertes is bent on killing Claudius and taking the throne as he bursts on the scene in 4.5. Of course Laertes does nothing. Later, Laertes confesses the desire to cut Hamlet's throat in the church yard. He actually gets his fingers on Hamlet's throat in 5.1 and again does nothing. They both have their reasons and excuses for not acting and thus highlight the gulf between being resolved to act and actually acting on the resolution. This is the main point of Hamlet's "to be" speech. Revenge is merely the vehicle to carry the heavier dichotomous themes of human weakness. All those with dead fathers in the play feel the blood lust for revenge. Be it Hamlet and Laertes or Prince Fortinbras and Pyrrhus. All delay their revenge. Prince Fortinbras goes so far as to forgo his revenge and his success at the end of the play is his reward.