This is Hamlet's third soliloquy. In his first soliloquy, in act 1, scene 2, Hamlet questions his existence, grieves his father's death, tortures himself about his mother's hasty marriage to his uncle, Claudius, and decides that "It is not, nor it cannot come to, good" (1.2.161).

In his second soliloquy, in act 1, scene 5, after he's encountered his father's ghost and been told that Claudius killed his father, Hamlet calls his mother "a most pernicious woman" and his uncle a "damned villain" and passionately vows to avenge his father's murder.

HAMLET. ... Now to my word:
It is 'Adieu, adieu! Remember me.'
I have sworn't. (1.5.115-117)

By his third soliloquy, in act 2, scene 2, Hamlet has frightened Ophelia, mocked Polonius, played at words with Rosencrantz and Guildenstern, and amused himself with the players who arrive at Elsinore.

After watching one of the players perform a passionate speech about Hecuba from a play about Aeneas and Dido, Hamlet realizes that he's done absolutely nothing to even begin to avenge his father's murder.

Hamlet scolds himself for not being able to rouse his own passion even to the level of a player acting "but in a fiction, in a dream of passion" (2.2.545), and he cries out for vengeance.

Hamlet recognizes the futility of his ranting and emotional outbursts, and he puts the logical part of his brain to work. He decides to have the players perform a play "something like the murder of [his] father" (2.2.590) so he can observe Claudius's reaction to the play and hopefully observe him acting guilty about murdering Hamlet's father, if what the ghost said is true.

For some reason, Hamlet second-guesses what the ghost said to him—something about the ghost being a devil and abusing Hamlet to damn him—and Hamlet is looking for more or better proof that what the ghost told him is true, even if that proof is likely to be wholly subjective, indirect, and circumstantial, at best.

This isn't the only time that Hamlet procrastinates about avenging his father's murder, of course, but it comes fairly soon after his previous soliloquy, in which he swore to put everything aside and focus entirely on vengeance against Claudius.

In his third soliloquy, Hamlet berates himself for his indecision, his inaction, and his cowardice. The theme of this soliloquy is Hamlet's depression.

Hamlet reflects upon the emotion "that this player here" has been able to summon. This emotion is only theatrical, and it is "all for nothing,/For Hecuba"(2.2.514) that he stirs his feelings whereas Hamlet has a dead father's ghost that cries for revenge and he has yet to do anything. Wondering what this actor would do if he were in the situation of talking to his father's ghost, Hamlet decides that this man would swear and drown the stage with tears. Furthermore, he would stir others so much that he would "make mad the guilty and appall the free..." (2.2.520)

Hamlet continues to wonder at his procrastination in avenging his father's murder. He berates himself as "a dull and a muddy-mettled rascal" (2.2.526) who mopes around and procrastinates in avenging his father's death. "Am I a coward?"(2.2.530) he asks himself. Hamlet then tries to bolster his courage and get control of his emotions. He finally decides that he may be able to detect Claudius's guilt if the new king watches a play that imitates what he might have done. "The play's the thing/ Wherein I'll catch the conscience of the king." (2.2.566-567)

At this point, Hamlet decides to take action cleverly. He has been reluctant to act because he has not been sure that King Hamlet's ghost has not been the devil merely tricking him. But, if Claudius reacts with emotion to the play that reenacts the murder of his father, Hamlet can be sure that the spirit who talked to him was, indeed, his father's ghost.

This soliloquy from act 2, scene 2 of Hamlet emphasizes Hamlet's disgust with himself, his ability to procrastinate, and his inability to exact immediate revenge for his father's murder against his uncle, Claudius.

Hamlet plans to have the Players enact a play that will resemble the actions of Claudius when he murdered King Hamlet. Yet, Hamlet castigates himself when he states:

Why, what an ass am I! This is most brave,
That I, the son of a dear father murder'd,
Prompted to my revenge by heaven and hell,
Must, like a whore, unpack my heart with words (556-559).

Even though he has plan, he realizes that he is still not taking the action necessary to remedy the situation quickly. This soliloquy furthers the theme of Hamlet's inability to act decisively. Just like his feigned madness, he distances himself from the immediacy of the situation. He calls himself both a "coward" and an "ass," yet he still does not spur himself on to revenge. In this manner, he ends the soliloquy with the following:

The play's the thing
Wherein I'll catch the conscience of the king (579-580).

Again, Hamlet resorts to ploys which may or may not work rather than taking matters into his own hands.

The main message of this soliloquy is that Hamlet feels like a total lowlife for having done nothing so far to avenge his father's murder. Hamlet has just heard an actor recite a monologue about Pyrrhus, the son of Achilles, and the actor appears to have shown more emotion—though he is only acting—than Hamlet has shown in his real life about his real tragedy.  Hamlet marvels that this actor could produce real-seeming tears, yet Hamlet neither says nor does anything so emotional. He feels he is a coward because he has been charged with the responsibility of exacting revenge on his father's murderer, but he has done nothing. Finally, toward the end of the speech, Hamlet decides to ask the actors to put on a play that is similar to the way his father was murdered, and he will watch his uncle while his uncle watches this play with the hope that he will reveal his own guilt. This monologue addresses themes such as cowardice, revenge, and guilt.