One of thefirst hints that something is rotten in the state of Denmark is when the viewer of Shakespeare's tragedy of "Hamlet" spots the appearance of Old Hamlet, haunting the castle at night.
Hamlet's father, walking the balustrades, looks as he did when he lived, but he is motivated by only once concern now-revenge. When the former king is finally able to open his heart to Young Hamlet, Old Hamlet tells his son that he is a spirit come from purgatory. During the day he must burn "fast in fires,Till the foul crimes done in my days of nature/Are burnt and purged away" while during the night he walks, hungry for revenge. The reason the former king is consigned to purgatory is because he died without making a full confession of his sins, as is required of all believing Christians.
While he was sleeping in his orchard, his brother poured poison in his ear, murdering him while he slept. To spur his son onto revenge his murder, the ghost plays upon Hamlet's already strong dislike of his uncle. The ghost makes reference to the perverted nature of the alliance of the "seemingly" virtuous Gertrude and Claudius, and calls Claudius "that incestuous, that adulterate beast." The ghost harps upon the "lewdness" of the queen's action, and also implies that Claudius is evil to turn a weak-willed woman to a "falling off" from a greater man to a lesser man. Hamlet thus is doubly motivated, the ghost implies, as his father's son and also as someone who should protect his mother from Claudius and from herself. The highly specific nature of how Hamlet's father met his demise lends credibility to the ghost's allegations. After all, the ghost does not merely tell Hamlet to "Revenge his foul and most unnatural murder," but tells Hamlet a means of murder that no one would likely surmise from the circumstances, unless he was a living or dead witne..