This is a crucial event in the story. It leads to Pip's becoming a gentleman and to the tragic conclusion with the death of Abel Magwitch. Pip robs his sister's pantry because he is so terrified of the escaped convict that he feels he must do so or be eviscerated. In the opening chapter the terrible convict threatens him as follows:
“You bring me, to-morrow morning early, that file and them wittles. You bring the lot to me, at that old Battery over yonder. You do it, and you never dare to say a word or dare to make a sign concerning your having seen such a person as me, or any person sumever, and you shall be let to live. You fail, or you go from my words in any partickler, no matter how small it is, and your heart and your liver shall be tore out, roasted, and ate."
Pip believes every word the escaped convict tells him. Furthermore, the convict makes him swear an oath that he will do as directed.
“Say, Lord strike you dead if you don't!” said the man.
I said so, and he took me down.
Pip believes that if the convict doesn't kill him for not keeping his promise, the Lord will strike him dead. He feels terribly guilty about stealing from his sister, but he believes he has no choice. So he takes the following items:
I stole some bread, some rind of cheese, about half a jar of mincemeat ...some brandy from a stone bottle...a meat bone with very little on it, and a beautiful round compact pork pie.
He also steals a file from among Joe's tools. He brings the booty to the convict in Chapter 3. Dickens' writing in these first chapters is magnificent. Pip has never seen any man eat the way this man eats.
He was gobbling mincemeat, meat bone, bread, cheese, and pork pie, all at once: staring distrustfully while he did so at the mist all round us, and often stopping—even stopping his jaws—to listen.
Inevitably Mrs. Joe Gargary discovers that her pantry has been robbed. But Pip is saved from her wrath when the convict takes the blame on himself in order to spare Pip.
So,” said my convict, turning his eyes on Joe in a moody manner, and without the least glance at me;” so you're the blacksmith, are you? Then I'm sorry to say, I've eat your pie.”
This is the last Pip will see of the convict until Chapter 39, when Abel Magwitch comes to him in a howling storm and reveals that he is the benefactor responsible for making Pip into the gentleman he has become. Magwitch had been so grateful to Pip for bringing him that food and brandy that he had sworn to repay Pip by sending money from his exile in far-off Australia to have him educated and turned into his idea of a real London gentleman, which was really nothing but a snobbish and useless fop with fine clothes and fine manners. Magwitch hadn't realized that little Pip was acting out of pure terror and not out of pity or generosity when he brought him that banquet at the churchyard in Chapter 3. He tells Pip in Chapter 39:
“You acted nobly, my boy,” said he. “Noble Pip! And I have never forgot it!”
When Magwitch moves in with Pip and his friend Herbert, Pip will notice that Magwitch still eats in the same animalistic manner as he was eating in Chapter 3. But by this time Pip has become a fastidious London gentleman, and he is so repulsed by Magwitch's "heavy grubbing" that he is unable to eat anything himself. Ironically, Pip himself had had very bad table manners when he first arrived in London, and he had to be gently instructed by Herbert Pocket.