Mr. Wopsle says that the prodigal son in the Bible was accompanied by swine after Joe gives Pip more gravy at dinner. The adults at the dinner, including Pip's sister, constantly demean Pip. Only Joe is generous and loving to Pip and shows him this love not by speaking out but by constantly providing Pip with more gravy.
In chapter 18, Mr. Jaggers arrives to tell Pip and Joe that Pip has come into a fortune, and Mr. Jaggers offers to pay Joe for getting Pip out of his apprenticeship. Joe refuses to take any money and says that he will not stand in Pip's way.
Dickens includes these two scenes as a precursor of what is to come. Pip will eventually be the prodigal son who will return home to Joe without any money, and Joe will take him back lovingly. These two scenes set up Pip's return, as he is first compared to the prodigal son, and later, in chapter 18, Joe is shown feeling sad that Pip is leaving, as he cares for Pip greatly.