The narrator describes Hester in very complimentary language; the connotation of all of his word choices and imagery is incredibly positive. She has a "figure of perfect elegance" and "abundant" hair that is so "glossy" that it reflects the sunlight. Her face is "beautiful" and her complexion has a "richness" that sets off her "deep black eyes." She is likewise "ladylike" and "feminine," conducting herself with grace and "dignity." All of these descriptors are incredibly positive, even effusive.
Further, rather than being dimmed by her terrible ordeal, "her beauty shone out, and made a halo of the misfortune and ignominy in which she was enveloped." Thus, she is compared, via metaphor, to a divine being, like an angel. This is a rather ironic comparison, too, since we would typically not expect that a woman being punished for a terrible sin would be associated with the faultless divine. This helps us to understand that the narrator's assessment of Hester Prynne and her "sin" is dramatically different from her peers in the story, and this likewise helps lead to the conclusion that we are supposed to disagree with the majority of the Puritan population as well.
Moreover, the narrator says that the beautifully-wrought scarlet letter on Hester's breast "had the effect of a spell, taking her out of the ordinary relations with humanity, and enclosing her in a sphere by herself." The comparison of the letter's effect to a spell's effect, via metaphor, separates Hester from everyone else, and further compels us to sympathize with her in her "desperate recklessness" at being made such a spectacle. While the narrator considers her to be more like an angel, her community thinks of her as something more akin to a witch.
Thus, through Hawthorne's imagery, connotation, irony, and metaphors, we get a sense of Hester as a strong, beautiful woman who is judged unnecessarily harshly by her community. We immediately begin to sympathize with her as a result of his carefully-chosen language.