Chapter XXXIX records the most momentous event in Pip's entire life. This is where he learns that Magwitch, and not Miss Havisham, has been responsible for all his great expectations.
All the truth of my position came flashing on me; and its disappointments, dangers, disgraces, consequences of all kinds, rushed in in such a mutitude that I was borne down by them and had to struggle for every breath I drew.
Poor Magwitch is proud of himself for turning an ignorant country boy into a London gentleman and does not realize how horrified Pip feels, perhaps especially at the realization that Miss Havisham had not become his patron with the intention of grooming him to marry Estella.
"Yes, Pip, dear boy. I've made a gentleman on you! It's me wot has done it!....I lived rough, that you should live smooth; I worked hard that you should be above work."
Magwitch's idea of a gentleman is a soft, lazy man who has lots of money to spend and doesn't have to work for it. Pip has become what Magwitch has made of him.
Pip doesn't want to take any more of Magwitch's money because he sees how the underprivileged of this world look up to gentlemen and ladies who, like Pip himself, are only selfish, useless parasites. Magwitch's joy in creating his very own gentleman only makes Pip realize what he has become--a fop infatuated with a "lady" who is no better than he is and idolizing a selfish old woman who let him believe she was his benefactress when she was only tossing him a few coins. The rich do not get rich by giving money away.
What saves Pip is his working-class background. He is not a "real" gentleman--not completely spoiled by idleness and privilege--but a sort of half-gentleman who still retains the virtues and values he acquired from Joe Gargary and to some extent from Biddy.
Gentlemen and ladies act the way they do for self-protection, to erect barriers between themselves and the lower classes. We can see in Great Expectations the pervasive influence of the French Revolution, with its ideals of liberty, equality, and fraternity--an epoch-making event Dickens wrote about in his novel A Tale of Two Cities, which begins with the wonderful words:
It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair....
Dickens was not a revolutionary or a nihilist but a religious man whose writings undoubtedly did more to change social conditions on both sides of the Atlantic than the preachings of any number of revolutionaries.
When Pip learns that Magwitch (the convict whom he met at the marshes and whom he helped) is his benefactor, not Miss Havisham all his great expectations perish, marking a climax in the novel.
For an hour or more, I remained too stunned to think; and it was not until I began to think, that I began fully to know how wrecked I was, and how the ship in which I had sailed was gone to pieces.
Miss Havisham's intentions towards me, all a mere dream; Estella not designed for me; I only suffered in Satis house as a convenience, a sting for the greedy relations, a model with a mechanical heart to practise on when no other practice was at hand; those were the first smarts I had.
Yet, realizing his snobbery, he tries with all his might to save Magwitch.
For now my repugnance to him had all melted away, and in the hunted wounded shackled creature who held my hand in his, I only saw a man who had meant to be my benefactor, and who had felt affectionately, gratefully, and generously, towards me with great constancy through a series of years. I only saw in him a much better man than I had been to Joe.
This self realization of Pip makes him understand that Social status has nothing to do with a gentleman, and a true gentleman is who he is good at heart. Thus he gives up his faulty efforts in becoming a gentleman and works for the well being of Magwitch.
So he refuses to take no more money from Magwitch.