The ghost does not speak in the first scene, but later talks of his afterlife: "Doomed for a certain term to walk the night". Horatio also talks of the ghost starting like "a guilty thing upon a fearful summons". This summons is purgatory, a state between heaven and hell where those who have not repented before their death have their "foul crimes...burnt and purged away". This is a religious belief present in Catholicism but not Christianity. Therefore, the strong religious theme of forgiveness does not have the same relevance today. Hamlets father was "cut off even in the blossoms of (his) sin": he was killed before he had repented. Claudius also tries to repent: "what form of prayer can serve my turn?” but also questions whether keeping the crown or his wife stands in the way of forgiveness: "May one be pardoned and retain th'offence?". Hamlet chooses not to kill Claudius: "Now a is a praying...and so goes to heaven". Hamlet believes him to be "fit and seasoned for the passage". In fact he isn't ("words without thought never to heaven go") and perhaps Hamlet knows this and is just procrastinating, but the quotes illustrate the weight given to the afterlife, with it’s possibilities considered or displayed in many of the main characters. Today, the afterlife is not such an important theme, especially due to our diminished belief in purgatory. The practice of praying to repent for sins is still practiced widely in Christianity, and so this at least can be understood. Purgatory, too, can be understood in the Elizabethan sense from the descriptions throughout Hamlet, illustrated by many of the above quotes, making a complete understanding of it beforehand unnecessary.
Marriage has changed dramatically in the last 4 centuries. The first divorce of the Church of England (Henry VIII) occurred just outside of Shakespeare’s lifetime; now divorces are very common. The reduction in religious beliefs means today marriage carries less of a religious aspect. Hamlet obviously considers these vows important when he scolds his mother for making "marriage vows as false as dicers oaths". Today, though, we can still appreciate the insensitivity in Gertrude marrying her brother in law so quickly: "The funeral baked meats did coldly furnish the marriage tables". Hamlet has very strong views on this marriage, illustrated when he organizes the play to "catch the conscience of the king". The 'Player Queen' makes a long speech about the sanctity of marriage and the sin of remarrying: "None wed the second but murdered the first". Hamlet also scolds his mother for forgetting so quickly her previous husband: "A beast that wants discourse of reason would have mourned longer". Later Hamlet asks his mother "What devil was't that hath cozened you at hoodman blind", implying that the devil was working in Gertrude when she remarried. Today, a widow remarrying would not be frowned upon, but within that time span and with the dead husband's brother it certainly would be. In the 17th Century it was frowned on by Hamlet, perhaps more because of the disrespect for the marriage vows shown by Gertrude, substantiated by his previous reference to the devil. A similar situation occurred under a century before, when Henry VIII blamed his failure to father a male heir on God's anger at him marrying Catherine of Aragon, his brother's widow. The point in effect, then, remains the same but for slightly different reasons. With respect to an understanding of Hamlet, the marriage vows are today much the same as they were then, and today we can understand that Hamlet is disgusted by the betrayal of these vows.
Suicide is the area that draws the most different comparison between then and now. For Shakespeare's audience, suicide was considered an insult to the life God had blessed them with. Therefore, it was severely frowned upon. Ophelia's "death was doubtful", and so the priest does all he can to keep the body from receiving the treatment a suicide victim would normally suffer: "For charitable prayers, shards, flints and pebbles should be thrown on her". If Ophelia "had not been a gentlewoman, she should have been buried out of Christian burial", the clowns tell us as they dig her grave, allowing her to avoid being buried in "grounds unsanctified". Today, we feel less strongly about the religious aspect of suicide, and it has become much more common. Those that do commit suicide are also less likely to be religious, and so do not consider as deeply the afterlife as Hamlet does, or damn suicide victims as they did. In Hamlet's first scene he wishes "O that this too too solid flesh would melt", and later questions himself "To be or not to be". Hamlet ponders what fate may face him if he were to end his life: "in that sleep of death what dreams may come". He also weighs up two options, does he "suffer the slings and arrows of outrageous fortune" or "take arms against a sea of troubles"? As a religious man, Hamlet believes in the damnation that comes with suicide, but does not consider hell, rather an "undiscovered country", opening up the possibility that Hamlet is questioning his faith. Analysts have also questioned whether Gertrude drinks the poison intended for Hamlet on purpose (as an escape from the situation Claudius has brought her to) or not. Even Horatio considers suicide too, so it is an undeniably strong theme. The weight of the decision to commit suicide then was far greater, and so it has to be seen in this context when so many characters consider or commit suicide. Our understanding of it is far removed from the heavily religious view of Shakespeare's time. Hamlet's soliloquies therefore carried a much more ominous weight then, when instead of mere death, suicide meant eternal damnation.
In conclusion, knowledge of the basic religious beliefs of Shakespeare's time is important, because many of the play's themes are based around Christianity. Today, religion is undeniably less relevant and less practiced in our society, but generally this does not drastically alter our understanding of the religious morals or teachings displayed in Hamlet. The strong religious aspect of suicide, and to a lesser extent the theory of purgatory, are two main themes a modern audience will not be familiar with, certainly not in the way a contemporary audience would have been. This makes a basic understanding of these specific religious beliefs vital.