In The Scarlet Letter, Nathaniel Hawthorne takes the simple idea of a forest and turns it into a symbol that creates the sense of a supernatural presence of evil around the small township in which his characters live.
Writers use symbols in their work to represent key ideas that go beyond the actual physical reality of the objects (or sometimes people, places, or events) they include in their narratives.
In The Scarlet Letter, today’s reader may not be able to fully relate to the social conditions that forced Hester Prynne to live as an outcast and Reverend Dimmesdale to punish himself with guilt, but because of Hawthorne’s effective use of symbolism in depicting the forest that borders the town, they can get still a strong sense of the evil that hides in the community, and this social evil is something that most readers probably can relate to in some way.
One night, about halfway through the story in chapter 12, Reverend Dimmesdale is overcome with guilt over his role in Hester’s predicament (he is the unknown father of Pearl--the man who committed adultery with her). He ascends to the scaffold, where Hester had stood in shame before the town as part of her punishment in chapter 2. In his misery, he lets out an involuntary cry. He believes that this cry will alert the town to his presence on the scaffold and thus reveal his guilt. But there is very little reaction to the cry; a few people come to their windows but do not see Dimmesdale on the scaffold. However, one important character’s perception of the scream is detailed by Hawthorne—the Mistress Hibbins, suspected by many of witchcraft:
"Beyond the shadow of a doubt, this venerable witch-lady [Mistress Hibbins] had heard Mr. Dimmesdale’s outcry, and interpreted it, with its multitudinous echoes and reverberations, as the clamor of the fiends and night-hags, with whom she was well known to make excursions into the forest."
With this passage, Hawthorne links Hibbins, the witch-lady, to the forest, along with “fiends” and “night-hags.” This establishes the idea that the people of the town are surrounded by a presence of evil. The reader by now also has gained a sense that this evil can infect the town, as we see how the good-hearted Hester is vilified by some of the townspeople.
A little later, in chapter 16, Hester and Pearl venture into the forest, hoping to encounter Dimmesdale. Pearl asks her mother to tell her a story about the Black Man who supposedly lives in the forest:
". . . he haunts this forest and carries a book with him—a big, heavy book, with iron clasps; and how this ugly Black Man offers book and an iron pen to everybody that meets him here among the trees; and they are to write their names with their own blood."
That fact that Pearl, a young child who has little communication with the other children of the town, knows this story reveals how important the idea of this forest-evil is to the town. They see themselves as a people surrounded by the danger of evil, but at the same time are unaware of their own evil thoughts and actions, as evidenced by their treatment of Hester and Pearl.
Because he has characterized the forest in this way, Hawthorne has created a symbol that enables the reader to feel the presence of this evil every time he mentions the forest.