What is the meaning of Hamlet's soliloquy, "How all occasions do inform...," in Act 4, Scene 4?
Hamlet watches the army of the Norweigan, Fortinbras, and asks a Captain where they are going. The Captain tells him that the Norweigans march to "gain a little patch of ground" which is barely worth five ducats. The army of men are about to pointlessly sacrifice their lives for a seemingly worthless gain.
Starting from this point, Hamlet's soliloquy considers the way that everything he experiences ("all occasions") seem to point toward the revenge regicide--dulled by inaction, "dull revenge"--that he has thus far been unable to commit against Claudius.
Hamlet ruminates on the nature of humankind's God-given reason and concludes bitterly that he does not know why he remains alive saying that "this thing's to do" but still not doing it, a remark that makes explicit the dichotomy between thought and action that many critics have found in the play as a whole.
As he did in his earlier soliloquy ("Oh what a rogue and peasant slave..."), Hamlet considers that, unlike these soldiers, he has a "great argument" (compelling reason) to carry out his deed of vengeance, but, unlike these men, he seems unable to do it.
Hamlet's conclusion is that, from this moment forth, "my thoughts be bloody, or be nothing worth" though we might detect a wry irony of Shakespeare's in the line: Hamlet, who is supposed to be doing has just resolved to think bloodily, rather than act bloodily.
Hamlet is reminded by the King of Norway's resolve that he has been cowardly in pursuing his dead father's wishes for revenge regicide against Claudius. The King of Norway has shown, through his determination and desire for honor, that he is indeed kingly. By contrast with Hamlet's lack of resolve, he has made Hamlet realize how difficult all decisions are and yet how important it is that he follow through with his dead father's ghost's request to murder King Claudius. Hamlet berates himself for not using his God-given powers of reason; by not doing so, he wonders if he has sunk into a "bestial oblivion" or if he is plagued by "craven," or cowardly, "scruples." In other words, why can't he just simply kill Claudius the way his father wants him to? Hamlet wonders if he a coward?
In fact, he has killed Polonius and has been acting in such a semi-deranged manner that it is suggested to the audience that his knowledge about his father's murder is causing him to become more than a little insane, though his insanity is a point of strong debate amongst critics. Now, seeing how the King of Norway has the fortitude (a play on the name "Fortinbras," which means "strong arms") to take on a battle for the sake of honor and revenge, Hamlet is shamed into realizing that he must strengthen his resolve, he must focus his thoughts that must become "bloody" and murderous or "be nothing worth," or be worthless.
In Act IV, Scene 4, Hamlet rages against his own ability to seek revenge as the Ghost has urged. He sees the army of Young Fortinbras, who are willing to go to their death "even for an eggshell," and it reminds him of his "dull revenge" and that he has lost his sense purpose.
Hamlet also contemplates the difference between man and beast (animal): If all he is to do is "sleep and feed," then Hamlet feels he is no better than an animal. He must use his ability to think and plan.
The soldiers give him reason to think about his own honor, with "a father kill'd, a mother stained," and this thought rallies him to action: "From this time forth, my thoughts be bloody." This soliloquy, then, refreshes Hamlet's purpose in seeking revenge.
This soliloquy represents the turning point. Hamlet conceives a way to prove Claudius murdered his father through a play. Up until this time, Hamlet was without direction. Thereafter, he is focused on the plan he has conceived in this passage.
Interestingly, in the Hollywood film version of Hamlet with Sir Lawrence Olivier, this soliloquy was omitted, showing how little Hollywood understood Shakespeare.