In having to enter and act in the world of his uncle, Hamlet himself becomes an unwilling creature of that world. When he chooses to obey the ghost's command and revenge his father, Hamlet accepts the inevitability that he must become part of Denmark's "unweeded garden". As the ripple of original vengeful intent widens and Hamlet is slowly but surely entangled in Claudius' brutal world through his madness, his murders, his plots, his relationship with other characters and his revelations on life and more importantly, death.
Even before the ghost urges Hamlet to avenge his death, Hamlet teeters on the edge of his uncle's brutal world. Whilst never evil in intent Hamlet is simply one of the finest tragic heroes. Caught between his agony of mind and indecision Hamlet's nature is neither treacherous like Claudius' nor rash like Laertes'. This combination of values carries only tragedy when one such as Hamlet suffers such a fate as he did. Prior to his dead father's prompting, Hamlet is already devoured by melancholy over the loss of Old Hamlet and his mother's "o'er hasty" marriage to Claudius. This suggests that Hamlet was already inexorably linked to his Uncle's brutal world.
"It is not, nor it cannot come to good."
Hamlet also feels jealousy towards his mother as their relationship goes beyond that of a normal parent/child relationship. Whilst perhaps not sexual, their mere fifteen years age difference has enclosed them in a very close-knit co-dependant affair.
"You are the Queen, your husband's brother's wife,
And, would it not so, you are my mother."
This jealousy and hatred Hamlet feels is close to pushing him over the edge, so when the Ghost commands revenge Hamlet has already positioned himself at the starting line ready to begin his descent into Denmark's brutal court.
Hamlet's acceptance of the task of revenge, even if somewhat reluctant, is the key to entering Claudius' world. Revenge in any context is morally...