The narrator of The Mayor of Casterbridge focuses mainly on the four central characters: Michael Henchard, Elizabeth-Jane, Donald Farfrae, and Lucetta. The narrator moves in and out of these characters' minds, explaining their motivations, plans, and disappointments to the reader.
The narrator understands the characters better than they understand themselves. Even when a character makes a mistake (which happens a lot), the narrator seems to understand where the character is coming from. As a result, the reader often finds him or herself feeling sympathy for the characters even when they're screwing up big-time.