Dickens appeals to the reader's sense of pathos through Esther's innocent and childlike diction. For example, when the reader first "meets" her in Chapter 3, she explains that
I had always rather a noticing way – not a quick way, O no! – a silent way of noticing what passed before me, and thinking I should like to understand it better. I have not by any means a quick understanding. When I love a person very tenderly indeed, it seems to brighten. But even that may be my vanity.
Earlier in this section Esther tells the reader she is "not clever," and she elaborates here that her "noticing way" is merely a method of trying to gather as much information as possible, as she has "by no means a quick understanding." Her roundabout, often self-deprecating, and unassuming way of explaining her role in situations makes her deeply sympathetic to the reader.
Her language in the "Esther's Narrative" sections of the novel is full of appeals to the emotions, connecting her with values presumably common to Dickens's audience. Esther "speaks" directly to the reader, like all first-person narrators, but she also makes modest little interjections; her "O no!" here amplifies her statement that her way is not "quick" (clever). This brings the reader closer to her as a storyteller, and also belies the fact that a lot of her narrating is very clever indeed.
This use of pathos also conceals, at least for a while, that Esther is something of an unreliable narrator; her "memories" in Bleak House are swayed by her feelings. She also conceals some of those feelings from the reader. For example, she doesn't let on her affection for Mr. Woodcourt until well after he is introduced.
