nteacher's answer above is undoubtedly correct. It would seem that Hamlet must be making such a lengthy inquiry because the ghost is not immediately responding to him. Perhaps the ghost keeps moving and Hamlet has to pursue it. Hamlet has to keep essentially asking the same thing until the ghost finally decides to speak. The ghost has previously refused to say anything to the guards, and the audience might be held in suspense wondering whether the ghost is ever going to say anything, whether it is even capable of speaking, what it will sound like if it does speak, and what it might say. At this point we do not know--or at least Shakespeare's audience did not know--that the ghost has astonishing information of the gravest importance to communicate. One possible reason that the ghost takes so long about addressing his own son might be that he wants to be sure that nodoy but Hamlet will hear what he has to say. If Claudius even suspected that Hamlet had been communicating with his father's ghost, then Hamlet's own life would be in imminent danger.
Essentially, Hamlet just wants to know why the Ghost has appeared. He recognizes the apparition as the spirit of his father, and wonders why he has appeared. His tone, using such phrases as "horridly shake our disposition," references to the dead king's bones, and the "hideous" night, suggest that he is very frightened, first by the ghost himself, but also by the fear that its appearance is evidence of some sort of terrible misfortune to come. So Hamlet is both filled with terror and with insatiable curiosity, and both of these sentiments are expressed in his address to the Ghost, as well as his willingness to follow him over the objections of his friends.