As there are different editions, the passage about the slab is found here on enotes at the end Chapter XXXVIII.  In this chapter, which is near the conclusion of Stage II of Great Expectations,  Pip, who has been living in the hope of Miss Havisham's being his benefactor, extends this wish to the ultimate hope of his also being designated for Estella.  For this reward he has worked to become a gentleman who no longer the coarse, common laboring boy that she once insulted.

However, Pip attends the Assembly Ball and observes Estella whom he perceives as more beautiful than all the other young ladies. The object of the glances of Bentley Drummle, Estella tolerates this "blundering Drummle" to the extreme irritation of Pip.  When he asks her why she tolerates Drummle, alluding to the significance of her name, Dickens has Estella reply,

 “Moths, and all sorts of ugly creatures,...hover about a lighted candle. Can the candle help it?”

Pip is wretched that Estella tolerates Drummle, and even encourages him.  He realizes now that Miss Havisham has not been planning on his and Estella's union, and that Estella has no real love for him.  This realization for Pip is devastating as all his life he has dreamed of Estella's loving him.  Just as Estella tells Miss Havisham that the jilted woman has made Estella into what she is, Pip has fashioned himself from the polluted environment in which he has now lived some years.  As he realizes that all his efforts are futile, Pip alludes to the Eastern "story," the legendary One Thousand and One Arabian Nights.  In one story, Aladdin is a ragged child whom a wealthy stranger decides to use, and then kill. But, first the stranger gives Aladdin money, then he buys him clothes and invites the boy to accompany to the wealthy part of the city.  Finally, he shows Aladdin a flat stone with a ring attached to it.  He tells Aladdin to lift the ring on the stone and walk through the caverns where there is gold and silver.  He further instructs Aladdin to find a lamp and bring it to him. The magician knows that there is a magic lamp, but he cannot get it by himself because it will not work unless fetched by another.  So, he gives Aladdin a ring and encourages him to go. As Aladdin returns, the magician demands the lamp; however, Aladdin tells the magician he must help him out first. Just then, the slab slams shut and neither the magician on the outside nor Aladdin on the inside can move the slab.  Their fates are sealed.

In the story alluded to in Chapter XXXVIII, another slab is used to kill a sultan.  Pip compares himself to this sultan who has built his life only to have it destroyed.  With Estella's encouragement of Drummle, Pip feels his hopes of marrying her dashed. 

In chapter 38 of Great Expectations, Pip makes a great allusion to something called the Eastern...