This quote from Hamlet is a great one. In fact, one of the reasons I enjoy Hamlet so much is that so many notable quotes are found in the play, as well as great advice that ironically comes from Polonius who is a silly and foolish man—an unlikely candidate to be delivering such "pearls of wisdom."
The quote, "The play's the thing / wherin I'll catch the conscience of the King," is excellent first because of the rhyme. It's perfect. Second, Hamlet has been struggling so long with trying to avenge his father's death without losing his soul if the Ghost is not an honest one, that we can feel his exhilaration when he comes upon this stroke of genius…it will take a great deal of weight off of Hamlet's shoulders if the King will implicate himself while all Hamlet does is "doctor up" the play and wait. I have seen this line delivered with such gusto that even knowing the outcome of the scene and the play, there is hope in this comment, and after his father's death, Hamlet seems to have lost all his hope in the world. It is a fine line!!
Another reason the passage is effective is that it introduces action to follow and builds suspense. It creates a "wait for it" moment in the play as Hamlet's scheme is about to unfold. Will his clever plan work? How will Claudius react? What will Hamlet do if/when Claudius does react strongly to the players' rewritten performance? At this point, the audience is inspired to imagine what is about to happen and can't wait to find out for sure. Great drama!
As Amy-lepore has said this is "psychology at it's best." There is another element in that it plays directly into the long delay (we as readers perceive) between Hamlet's charge to avenge his father and the action that requires. Hamlet struggles to come to resolution, and this play is one more element in which he seeks the path which he should take. And yet, when the play shows what Hamlet perceives as Claudius's guilt, he does not go right out and avenge his father's death. There is even more delay.
I love it since Hamlet is convinced that men can lie with words, but their body language and facial expressions tell all. Up to this point, Hamlet has been trying to decide if the ghost speaks true about Claudius. He is attempting to made up his mind to either act against his uncle or disregard his father's ghost. The play, which has been rigged to reveal the story according to the ghost, will convince Hamlet of Claudius' guilt or innocence based on the King's reaction and response. It's psychology at its best!
I think the attraction is at least partly down to the way in which it explores the way that theatre and drama can mirror our own feelings and emotions. Just as Claudius has his guilt exposed through drama, so we too can have our own fears, hates, loves and joys exposed. Vicariously seeing others experiencing them is one way which adds to our own appreciation of the condition of being human.
Part of the appeal of the line is the use of the concise rhyme in the short sentence. After listening to the first part of the speech with its many long sentences that employ multiple clauses, this line stands apart as clear and direct. We know exactly what he means!
I think that this quote has become popular not because it has any huge significance to the play, but because it seems like a promotion of the idea that theater is important.
You can easily imagine the play being just as good without this line. It would still be clear that Hamlet is using the play to make Claudius
The line has become very famous without the second part of it -- we all know it simply as "The play's the thing," which seems to extol the importance of theater. Because the line has become this sort of a slogan, it is well-known and liked.
This quote from Act Two, scene two, in Shakespeare's Hamlet is appealing for several reasons. First, there is rhyme, which the ear picks up on. Next, Hamlet is in high spirits, believing this will be the perfect situation to find the proof he needs that the Ghost is an honest one (really his father, and telling the truth), and he will be able to finally fulfill his promise to his father's spirit.
This quote is significant in that Hamlet has rewritten a play and asked the players to act it out: it is actually Old Hamlet's murder they are portraying, and Hamlet is very excited by what he feels he has accomplished in devising this trap. (It is called Mousetrap, by the way.)
Hamlet has been very hard on himself about why he has taken so long to kill Claudius. He has watched the players who mourn Hecuba in their play, bringing forth tears that have no meaning—simply acting out their parts. Hamlet has more reason than anyone to mourn: his father was murdered, but Hamlet still has not killed Claudius. This quote is almost like a cheer on Hamlet's part as he speaks to himself—he feels that he has finally found a way to trick the shifty Claudius into revealing his part in Old Hamlet's death, and then Hamlet will be justified in killing Claudius.
In this section, Hamlet expresses concern about the honesty of the Ghost and how careful Hamlet must be (for he could lose his soul for wrongfully killing a king—a sin against God), but he also seems thrilled that he may have met the challenge of finding proof of Old Hamlet's murder. (You almost expect him to say, "I've got you now!")
The spirit that I have seen
May be a devil; and the devil hath power
T' assume a pleasing shape; yea, and perhaps (595)
Out of my weakness and my melancholy,
As he is very potent with such spirits,
Abuses me to damn me. I'll have grounds
More relative than this. The play's the thing
Wherein I'll catch the conscience of the King. (600).