SCENE V. Another part of the platform.
Enter GHOST and HAMLET
Where wilt thou lead me? speak; I'll go no further.
My hour is almost come,
When I to sulphurous and tormenting flames
Must render up myself.
Alas, poor ghost!
Pity me not, but lend thy serious hearing
To what I shall unfold.
Speak; I am bound to hear.
So art thou to revenge, when thou shalt hear.
I am thy father's spirit,
Doom'd for a certain term to walk the night,
And for the day confined to fast in fires,
Till the foul crimes done in my days of nature
Are burnt and purged away. But that I am forbid
To tell the secrets of my prison-house,
I could a tale unfold whose lightest word
Would harrow up thy soul, freeze thy young blood,
Make thy two eyes, like stars, start from their spheres,
Thy knotted and combined locks to part
And each particular hair to stand on end,
Like quills upon the fretful porpentine:
But this eternal blazon must not be
To ears of flesh and blood.
According to the Catholic Church, Purgatory is an intermediate state after death, between Heaven and Hell. Merriam Webster defines it rather neatly as a place "for expiatory purification; specifically : a place or state of punishment wherein according to Roman Catholic doctrine the souls of those who die in God's grace may make satisfaction for past sins and so become fit for heaven". It is very significant to Shakespeare's construction of Hamlet's theology (or, indeed, 'philosophy'.) The greatest poet to deal with Purgatory was Dante, in The Divine Comedy - although it appears very likely that Shakespeare never read Dante. (The Italian poet was not translated into English until the 18th Century). Dante conceptualised Purgatory as existing somewhere in the southern hemisphere. Rather closer to home for Shakespeare, there was reputedly an entrance to Purgatory on Station Island in Lough Derg, in the north west of Ireland. Pilgrims have been visiting this place for almost 1500 years.
As we discussed earlier, the Ghost clamouring for revenge was the most memorable part of whatever earlier version of the story existed on the Elizabethan stage. Shakespeare has the Ghost mention it rather quickly, before he waxes lyrical about how much he cannot speak about his place in Purgatory. Revenge will appear a great deal from now on - the Ghost has let it out of the bag, as it were.