Why does Pip go to stay with his Uncle Pumblechook in Great Expectations?

Pip goes to stay with Uncle Pumblechook before his first visit to Miss Havisham’s house.

Pip has no idea what to expect from Miss Havisham, but he does not like his Uncle Pumblechook.  Pumblechook is an arrogant blowhard, and does not treat Pip very well.  He agrees with Pip’s sister that Pip is certainly not to be coddled.

Besides being possessed by my sister's idea that a mortifying and penitential character ought to be imparted...

Pip goes to stay with Uncle Pumblechook before his first visit to Miss Havisham’s house.

Pip has no idea what to expect from Miss Havisham, but he does not like his Uncle Pumblechook.  Pumblechook is an arrogant blowhard, and does not treat Pip very well.  He agrees with Pip’s sister that Pip is certainly not to be coddled.

Besides being possessed by my sister's idea that a mortifying and penitential character ought to be imparted to my diet,—besides giving me as much crumb as possible in combination with as little butter, and putting such a quantity of warm water into my milk that it would have been more candid to have left the milk out altogether,—his conversation consisted of nothing but arithmetic. (Ch. 8)

Pumblechook constantly asks Pip to calculate math problems because he thinks that it is good for him.  He also takes credit for Pip’s excursion to Miss Havisham’s house.  She is a rich lady, and he and Pip’s sister think that visiting her house will somehow enrich him.

For such reasons, I was very glad when ten o'clock came and we started for Miss Havisham's; though I was not at all at my ease regarding the manner in which I should acquit myself under that lady's roof.  (Ch. 8)

As if Pip is not already having a bad enough time, Miss Havisham’s house is decidedly creepy and the inhabitants strange.  Pumblechook is not allowed to enter, Pip later determines that he never actually knew her.  He just pretended that he did.

Pumblechook tries to use Miss Havisham’s wealth to add to his reputation.  Actually, the visits to Miss Havisham’s house do seem to enrich Pip.  She pays to apprentice him to Joe, and then later comes into a grand inheritance.  He thinks it is from her, but it turns out it actually isn’t.