Why is Pip unable to recognize Joe’s intelligence?

When Pip receives a letter from Biddy that Joe will pay him a visit in London, the young gentleman demonstrates his newly-acquired snobbishness and reacts with "considerable disturbance and some mortification" as he becomes anxious about how Joe will be perceived by Herbert Pocket, his roommate, and especially by Drummle since this man would mock him. And, so, Pip comments,

throughout life, our worst weaknesses and meannesses are usually committed for the sake of the people whom we most despise.

Perceiving Joe through what Pip believes Drummle's vision would be, Pip finds Joe's awkwardness disturbing while the reader finds his attempts to balance his hat on the mantel amusing. Pip is embarrassed that Joe does not know how to properly use the tableware, forgetting in his snobishness that he himself had to be taught by Herbert. For Pip now, Joe appears backward and "common." Because of his discomfiture at embarrassing Pip, Joe falls into

unaccountable fits of mediations....and dropped so much more than he ate, and pretended that he hadn't dropped it; that I was heartily glad when Herbert left us for the city.

Keenly aware of the embarrassment that he has caused Pip, Joe tells him that he is out of place at the forge; he says that he will not return to London:

"Diwisions among such must come, and must be met as they come. If there's been any fault at all today, it's mine. You and me is not two figures to be together in London; nor et anywheres else but what is private, and benown, and understood among friends....You won' find half so much fault in me if you think of me in my forge dress, with my hammer in my hand, or even my pipe....And so God bless you, dear old Pip, old chap, God bless you!"

It is only after this speech, that Pip realizes Joe's wisdom and dignity. He narrates that

the fashion of his dress could no more come in its way when he spoke these words than it could come in its way in Heaven.

Pip has been blind to this dignity and intelligence of Joe because he has been concerned with people's appearances too much, and has placed value in appearances. Joe's illiteracy is an embarrassment for Pip as well as he manner of dress and speech.

Furthering the theme of Appearance vs. Reality, Pip is concerned in Chapter 28 with going to the forge and staying before he visits Estella at Satis House. He rationalizes that Joe might not be prepared to have him stay, and he might be too far from Miss Havisham's. But, the truth is that he feels it is not like a gentleman to bed at the forge; so, he stays at the Boar's Inn. Pip's snobbishness prevents him from the reality of Joe's intelligence and his unconditional love.