At the beginning of chapter XXVII, why doesn't Biddy read the last lines of the letter to Joe?
Having not allowed Joe and Biddy to accompany him to the stage that goes to London, Pip has already demonstrated his change in attitude about his home and those in it; he is embarrassed by them. When he arrives in London, Pip begins his transformation into what he thinks is a gentleman, but it is really a snob that he becomes. For, he is embarrassed by Joe who cannot read, Joe in his leather apron as a blacksmith, Joe who has no refinement whatsover. So, when Biddy writes that the loving Joe wishes to visit Pip, she is aware of his change in attitude towards his home and family. After she writes what Joe wishes to say, Biddy adds her own thoughts which she conceals from the proud Joe,
I hope and do not doubt it will be agreeable to see him even though a gentleman, for you had ever a good heart, and he is a worthy man.
With her female intuition, Biddy senses that Pip will be uncomfortable about Joe's coming to London, for there Joe will appear awkward and out of place, and thus be an embarrassment to Pip. Biddy realizes that Joe has bought gentlemanly clothing so he will not embarrass Pip; however, his awkwardness will mitigate the effect of the attire that he wears. So, she writes the words that she does, hoping to remind Pip of Joe's love and kindness, qualities deserving of Pip's respect and love in return.