What does Pip's new roommate do to make Pip believe Miss Havisham is his benefactor?Great Expectations by Charles Dickens

When Pip arrives in London with his "great expectations" of
becoming a gentleman he experiences one of the many coincidences in the novel: He again
encounters the pale young gentleman whom he fought at Satis House so many years ago. However,
this time there meeting is most amicable. For Pip finds Herbert Pocket most unassuming and
cordial. In fact, Herbert coaches Pip in good table manners. And, as they eat, Herbert relates to
Pip the history of Miss Havisham, whom Pip assumes is his
benefactress.

Herbert tells Pip two things that lead Pip to believe
that Miss Havisham has a vested interest in him. One of these is the fact that Herbert reveals
that he had been called to Miss Havisham's as a boy in order to meet Estella on a "trial
visit."

"...and if I
had come out of it successfully, I suppose I should have been provided for; perhaps I should have
been what-you-may-called-it to Estella.
[engaged]"

Now, Pip believes that he
is in the position to become engaged, so he may, then, be "provided for" as Herbert says. Also,
after Herbert relates the history of Miss Havisham, he promises Pip that he will not mention
anything about Pip's having been told not to ask or discuss to whom he owes his good
fortune,

"...you may be
very sure that it will never be even approached by
me."

When Herbert makes this remark,
Pip reflects,

He said
this with so much delicacy that I felt he as perfectly understood Miss Havisham to be my
benefactress as I understood the fact myself.

In this passage from Chapter XXII of
Great Expectations, the theme of Appearances vs. Reality is reiterated as
Pip gives credence again to the apparent truth of things.