In Chapter 57 of Great Expectations, why does Joe's treatment of Pip change as Pip gets well?
After the ordeal of saving Miss Havisham and getting burned and the long and the enervating attempts to save Magwitch from hanging, and his long vigil with poor Magwitch who dies from his injuries, Pip, heavily in debt, returns to his apartment and falls ill.
As he lies in bed wavering between delirium and consciousness, he, at last, perceives the face of his dear friend, Joe, and asks, "Is it Joe?" It is the old Joe who replies, "Which it air, old chap."
Guiltily, Pip expresses his shame and appreciation that Joe has come to nurse him. But, Joe explains that Biddy has encouraged him to waste no time in attending to Pip after he is notified of Pip's grave illness. As Pip gains some strength, Joe takes him outdoors. Pip recalls,
More composure came to me after a while, and we talked as we used to talk, lying on the grass at the old Battery. There was no change whatever in Joe. Exactly what he had been in my eyes then, he was in my eyes still; just as simply faithful, just as simply right.
However, as Pip gains his strength and returns to himself, Joe begins to withdraw the old familiarity; one day Pip remarks to Joe that he soon can walk by himself. And, Joe replies,
Do not overdo it, Pip...but I shall be happy fur to see you able, sir."
When Joe says "sir," Pip is disconcerted. He notes,
Joe became a little less easy with me. In my weakness and entire dependence on him, the dear fellow had fallen into the old tone, and called me by the old names, the dear “old Pip, old chap,” that now were music in my ears. I too had fallen into the old ways, only happy and thankful that he let me. But, imperceptibly, though I held by them fast, Joe's hold upon them began to slacken; and whereas I wondered at this, at first, I soon began to understand that the cause of it was in me, and that the fault of it was all mine.
Pip realizes that while he has been weak and ill, he has been again the little boy that Joe so loved. However, now that he has regained his strength, Pip is again the gentleman who shunned Joe on his visit to London. Seeing Pip as an adult again, thus, makes Joe uncomfortable and awkward around Pip. So Pip apologizes to him,
"We have had a time together, Joe, that I can never forget. There were days once, I know, that I did for a while forget; but I never shall forget these.”
Nevertheless, Joe departs, generously having paid Pip's debts, and having written to Pip that he does not wish to "intrude." Reading his letter, Pip knows that he must return to the forge, penitent as the Prodigal Son, and beg his forgiveness.