I do believe that the shade of that poor girl often hovers about that solemn nook – ay, though it is a church, a she was weak and erring. (53.16)
Last lines of the book, everyone! Must be important. And if you look at the "What’s Up With the Ending?" section, you’ll see more about this. Agnes was an outcast during her life because she was "weak and erring" (i.e., she had sex and got pregnant without being married). She wasn’t welcomed into the church or forgiven while she was alive, but Dickens suggests in these last lines that her ghost would be able to hang out there after she was dead. Does that mean that a "fallen woman" can only be forgiven by the church after she’s dead, or that while she was alive, the church was wrong to shun her?