Discuss Hamlet as a religious allegory.

Hamlet can be read as an allegory about the universal human problem of discerning between good and evil. Hamlet, a Christian, is faced with a dilemma from the moment the ghost of his father tells him that he was murdered by Claudius and that Hamlet must avenge his death.
In the Christian worldview, there is good and evil in the world, and doing evil, if one does not repent of it, leads to hell in the afterlife.
Hamlet therefore must discern if the ghost who visits him is truly his father or if he is a devil sent by Satan to tempt Hamlet to murder an innocent man. If Claudius did murder his father, Hamlet's conscience dictates that he must do the right thing and kill Claudius. If the Ghost is a devil, however, Hamlet's immortal soul would be in jeopardy for killing Claudius.
Hamlet is also allegorical in representing through Hamlet the universal human desire to evade taking responsibility for discerning and acting in response to evil. Hamlet is so upset about what faces him that he fantasizes about suicide as a way to escape having to determine whether or not to kill Claudius. Hamlet continues to hesitate even after he has established that the ghost told the truth.
Of course, Shakespeare being Shakespeare, the play questions the whole idea of violent revenge ever being the answer, leaving us with a stage full of dead bodies and a sense of lives wasted and cut short.