their own destruction. He remarks,

they did make love to this employment;They are not near my conscience; their defeatDoes by their own insinuation grow.

Rosencrantz and Guildenstern are childhood friends of Hamlet. From this perspective, we would expect them to be loyal friends to Hamlet who is going through a difficult time, but instead they are called by Claudius, Hamlet’s wicked uncle, to spy on him. We see this in act two scene two.

Hamlet immediately sees this point, and he distances himself from them. When Hamlet accidentally kills Polonius—who is hiding behind a curtain—Claudius grows more worried, and he tasks Rosencrantz and Guildenstern with escorting Hamlet to England. The pretense is that Hamlet could use some time away. Claudius's real purpose is to have Hamlet killed there.

Hamlet knows that something is off and finds the letter speaking of his death and rewrites the letter so that Rosencrantz and Guildenstern are killed instead. We actually do not know whether Rosencrantz and Guildenstern are in on the plot of murder.

When Hamlet finds out that they are dead, he says that he does not feel remorse.

They are not near my conscience; their defeat / Does by their own insinuation grow.

Rosencrantz and Guildenstern are murdered due to an ingenious plot masterminded by Hamlet. King Claudius instructed Rosencrantz and Guildenstern, Hamlet’s childhood friends, to escort him to England with official orders that Hamlet would be executed there. However, Hamlet discovered the king’s commission while on the ship to England and thus learned what was to be his ultimate fate. While Rosencrantz and Guildenstern slept, Hamlet rewrote the letter to say that Rosencrantz and Guildenstern, not Hamlet, should be executed. It was extremely fortuitous that Hamlet happened to have on his person his late father’s signet, which he used to reseal King Claudius’s letter and make it appear as if it had not been opened. Hamlet returns to Denmark, never making it to England, and explains to his good friend Horatio how Rosencrantz and Guildenstern met their end.

Hamlet explains to Horatio how he forged a letter to the English king in place of the one Rosencrantz and Guildenstern were delivering from King Claudius. As Hamlet tells Horatio, his forgery contained

An earnest conjuration from the King,

As England was his faithful tributary,

As love between them like the palm might flourish,

As peace should still her wheaten garland wear

And stand a comma 'tween their amities,

And many such like as's of great charge,

That on the view and knowing of these contents,

Without debatement further, more or less,

He should the bearers put to sudden death,

Not shriving-time allow'd.

So Rosencrantz and Guildenstern are unknowingly carrying what is known as a "bellerophonic letter." The term comes from Greek mythology. The hero Bellerophon, who was noted for taming the winged horse Pegasus, was asked to deliver a letter which unbeknownst to him contained a request that he be executed. One can imagine Rosencrantz and Guildenstern's surprise when they are taken immediately to the beheading block instead of being greeted with honors as emissaries from the King of Denmark. The two men would not know that the letter was a forgery because they would not see the letter and probably would not know the difference between Claudius' and Hamlet's handwriting anyway. Nevertheless, Hamlet requested

That on the view and knowing of these contents,

Without debatement further, more or less,

He should the bearers put to sudden death,

Not shriving-time allow'd.

This was to prevent the two unfortunate men from telling anyone, including a priest, anything about Hamlet's recent apparently mad behavior, including his murder of Polonius, or Claudius' fears for his own safety. Rosencrantz and Guildenstern probably do not know they are escorting Hamlet to his execution, nor do they know that the letter they are delivering is a forgery. They would probably both die believing that Claudius was having them beheaded for some offense of which they are unaware. If they had more time, they might confer with each other and guess that Hamlet had planted a forged letter in their packet--but Hamlet isn't giving them any time to think or to confer.

Ronsencrantz and Guildenstern (R & G) are somewhat mysterious figures in the play, as they are definitely old friends of Hamlet, but they are also definitely sent for by King Claudius to work for him to find out whether Hamlet is attempting to usurp the throne.  In the play, Claudius only mentions, upon their arrival in Act II, scene ii, the following:

The need we have to use you did provokeOur hasty sending.. . .I do entreat you bothThat being of so young days brought up with [Hamlet],That you vouchsafe your rest here in our court,. . .To draw him on to pleasures and to gather. . .Whether aught to us unknown afflicts him. . .

The King is good at veiled language, but, as the events of the play progress, R & G are revealed to the audience and Hamlet as sort of hired thugs meant to assist Claudius in getting rid of Hamlet.  This is most evidenced in Act IV scenes ii and iii.  And Claudius pronounces at the end of IV, iii that he intends to send Hamlet to England and to his death:

And England, if my love thou hold'st at aught,

. . .thou mayst no coldy set

Our sovereign process, which imports at full,

By letters congruing to that effect

The present death of Hamlet.

So, R & G are meant to be in conveyors of Hamlet to his death in England.  However, Hamlet outsmarts them.  Upon his return to Denmark in Act V, he relays to Horatio that he switched a letter condemning R & G to death with the one that they carried from the King condemning him.  In this way, the King of England put R & G to death in place of Hamlet.

For the quote from Act V relating this switch and more on Rosencrantz and Guildenstern, please follow the links below.