In this letter, Pip is being informed that his sister is dead. At this point, Pip is in London and his sister (Mrs. Joe Gargery) is still back in their hometown.
This is somewhat of a tough situation for Pip. He has pretty much abandoned Joe and Mrs. Joe since he has become a gentleman. He has not been back home since that time. When he does return for the funeral it will be his first time back.
Pip is forced to reflect on his life when his sister dies. He realizes that he has not been as caring as he should have been.