Is the Ghost honest?

Although rarely discussed throughout the discussion of Shakespeare's Hamlet, this scene introduces a very interesting topic and, in fact, one that is interwoven throughout the entire five acts of the play: is the ghost honest? Keep in mind the intense Roman Catholicism of the time and the teaching that any strange form (such as the ghost who is presumed to be Hamlet's dead father) is often explained as some unsettled soul from Purgatory. Purgatory, if the reader is unfamiliar with the teaching, is the place where souls not fully in the state of Grace must go to be "purged" or purified before they are able to enter heaven and experience the Beatific Vision of God. Roman Catholics are also quite familiar with the antithesis of the holy—the demonic. Hamlet invokes the Church teaching when he says that it might very well be "a spirit of good health," in other words one from Purgatory that has a job to do before entering heaven. Interestingly enough, Hamlet also invokes a different Church teaching when he says that the ghost just might be a "goblin damn'd," meaning a demon sent from hell in order to lead him astray. At this point in the play, readers remain unsure as to the nature and the honesty of this ghost. However, take note of the following things that are very interesting:
The ghost only appears at night (and on gloomy nights, at that).
The ghost "beckons [Hamlet] to go away with it. . . alone." None of Hamlet's confidants are allowed to accompany him. Does this mean the ghost has something to hide?
Hamlet's friends (who we already know are honest) urge Hamlet both emotionally and physically not to go with the ghost. Horatio is so adamant that he physically retrains Hamlet saying, "Be ruled. You shall not go."
As Hamlet leaves with the ghost, one of the most prominent quotes taken from the play is used by Marcellus: "Something is rotten in the state of Denmark." Truly, this is not the first time the reader must visit this idea of the question, "Is the ghost honest?" One must read the ghost's actual words and directive to Hamlet in order to decide further. This, of course, comes in later scenes of Shakespeare's play.