What is the role and significance of Mistress Hibbins in Nathaniel Hawthorne's The Scarlet Letter?
Toward the end of the novel, after Hester Prynne and Arthur Dimmesdale have determined to run away together, Hester sees Mistress Hibbins in town. Mistress Hibbins says a number of things that make it clear that she understands the relationship between Hester and Arthur. When Hester feigns confusion, Mistress Hibbins asks her,
"Dost thou think I have been to the forest so many times, and have yet no skill to judge who else has been there? . . . I know thee, Hester, for I behold the token. We may all see it in the sunshine! and it glows like a red flame in the dark. Thou wearest it openly, so there need be no question about that. But this minister! . . . When the Black Man sees one of his own servants, signed and sealed, so shy of owning to the bond as is the Reverend Mr. Dimmesdale, he hath a way of ordering matters so that the mark shall be disclosed, in open daylight, to the eyes of all the world!"
In other words, Hibbins claims that she knows sin and temptation well enough to know who else has experienced it. She says that though Dimmesdale tries to hide his sin, the Devil still knows of it. Her words even foreshadow the ending, where Dimmesdale finally confesses (sort of) and then dies on the scaffold.
Apparently Mistress Hibbins has known for a long time that Dimmesdale is Hester's co-sinner, and she has kept this knowledge to herself. It turns out, then, that she is more discerning as well as more compassionate than her Puritan peers. Those "self-constituted judges," as the narrator described them, wanted Hester branded or even hanged for her crimes. This society had little sympathy for her and was ready to treat her co-sinner the same way. Rather than "out" him, however, Mistress Hibbins has kept her knowledge to herself, reserving judgment because she knows that he will be judged by a higher power (though, for her, it is the Devil), in the way these so-called Christians ought to have done. The contrast between the so-called good, God-fearing Puritans and the godless witch actually makes the Puritans look even more self-righteous, officious, and merciless.
Mistress Hibbins, the sister of the governor of the Puritan colony, calls to Hester Prynne in Chapter VIII as she leaves the mansion of the governor,
"Wilt thou go with us tonight? There will be a merry company in the forest; and I well-nigh promised the Black Man that comely Hester Prynne should make one."
Mistress Hibbins, with her "ill-omened physiognomy" who appears to cast a shadow upon the governor's house, is, ironically, a witch. With the leader of the Puritan colony having a witch for a sister, Hawthorne's scorn for the hypocrisy of the Puritans is clearly apparent. In addition, that Hester refuses to accompany Mistress Hibbins because she "must keep watch over my little Pearl" or otherwise, she says, she would go and sign her name in the Black Man's book--"and that with own blood!"--is testimony to the validity of her plea that she be allowed to keep Pearl so she will live, and live righteously. Further, Hester's interview with Mistress Hibbins illustrates how dependent Hester has become on the child of her illicit love affair now that she has been ostracized from society.
Later in the novel, Mistress Hibbins appears at unexpected moments; each time that she does enter the scene, however, either Hester or Arthur Dimmesdale suffer from remorse. Thus it would seem that the witch serves as a reminder to Hester and the minister of their sin and of the darkness hidden in Puritanism.