Why does Hamlet delay? Give three instances and the reasons in his own language.

That's the timeless question of the play.  At the end of
Act 1, Hamlet accepts his ghost-father's command to get revenge against Claudius because
Claudius killed Hamlet's father. In Act 1, sc. 5, Hamlet tells Horatio, "It is an honest
ghost-". Later, though, in Act 2, sc. 2, Hamlet says, "The spirit I have seen / May be a
devil, and the devil hath power / T'assume a pleasing shape..." which indicates that
Hamlet isn't sure the ghost he spoke to was truly the spirit of his dead father and
that's the reason he hasn't carried out his revenge.  He goes on to say that he will
have the players perform a re-enactment of the killing as described by the ghost. 
Later, in Act 3, sc. 3, when Hamlet has seen by the king's reaction that he is guilty of
what the ghost described, Hamlet has the opportunity to kill Claudius when Claudius is
all alone in the chapel.  Hamlet doesn't kill him though because, as he says in lines
72-78, if he kills Claudius while Claudius is prayer, Hamlet fears Claudius's soul will
go to Heaven and Hamlet does not want that.  He wants Claudius's soul to go to hell.  In
Act 4, sc. 4, Hamlet once again rails against himself and his lack of action saying that
he is not sure why he has delayed except that he overthinks the situation: "...Now
whether it be / Bestial oblivion or some craven scruple / Or thinking too precisely on
th' event....".  Even Hamlet does not seem to be clear about why he delays in getting
revenge.