It could be said that Hawthorne uses symbolism for two major reasons. One is that the use of symbolism creates a heightened effect, rendering the story more memorable with the images of dark and light, good and evil, nature and society, freedom and oppression.
Symbolism also lends the novel an intriguing air of ambiguity, leaving open the possibility of several interpretations. For instance, the forest where Hester meets her secret lover Dimmesdale, is rendered as a dark place of sin from a Puritan viewpoint, but can also represent the freedom and wildness of nature and instinct, released from the severe restrictions of Puritan society. As for the scarlet letter itself, its implications too are various. For the Puritans it is a symbol of shame, but it could also be taken as a positive symbol of Hester's defiance, and so on.