As the pivotal pillars of the drama, Hamlet's soliloquies are what direct the action of the play. For, in them the Prince of Denmark deliberates greatly on his own feelings and what course he should take after the ghost of his father entreats him to avenge his murder.
In his third soliloquy in Act II, after Rosencrantz and Guildenstern have departed, Hamlet chides himself for his procrastination--"O, what a rogue and peasant slave am I!"--when he should be acting on his father's request. Contrasting himself with the player who sheds tears as he recites the tragic lines about Hecuba's grief over the death of her husband from a play about the fall of Troy, Hamlet asks himself why he cannot rise to action with the motives and passion he has that should easily give him cause for vengeance. "But I am pigeon-liver'd and lack gall," he reviles himself. Finally, he turns his anger against Claudius, calling him a "bloody, bawdy villain"; furthermore, he decides to test Claudius by having the players act out something like the murder of King Hamlet and watch his uncle's reactions. This, Hamlet hopes, will convince him to act as he will have proof of the guilt of Claudius: "The play's the thing."
Thus, the theme, of this soliloquy is Hamlet's emotion vs. his rationality. For, while his melancholic soul prevents him from acting, after observing the player who is able to summon emotion from the lines of a mere ficitional work, Hamlet's mind reasons that he must shake himself " Out of my weakness and my melancholy" and seek retribution for his father's murder by first verifying that Claudius is, indeed, guilty.