Symbolism, Imagery, Allegory
The woods are just trees/ The trees are just wood!
With all due respect to Stephen Sondheim—if there's one thing we know about the woods in fairy tales, it's that they're not just wood. Take Little Red Riding Hood. (Yeah, we know that this comparison would probably make young Goodman Brown roll over in his fictional grave. But we're going to do it anyway.)
• Like Little Red, Goodman Brown takes a journey through a forest.
• As for Little Red, the forest is a place where everyday assumptions get overturned. Grandmothers turn into wolves, kindly old women turn into witches.
• And both of them come home from their journey knowing that a cape and a hood won't protect them.
It doesn't take M. Night Shyamalan to tell us that the woods are frightening. Where Salem is orderly and civil, the woods are confusing and nightmarish:
the traveler knows not who may be concealed by the innumerable trunks and thick boughs overhead, so that, with lonely footsteps, he may yet be passing through an unseen multitude. (8)
Yep, this is one freaky place. So, the woods definitely symbolize the world outside: outside the village, outside the normal boundaries of right and wrong, outside of Brown's comfort zone. But they could symbolize something else, as well: they could be an embodiment of young Goodman Brown's fears and suspicions, a freaky picture of dark feelings he doesn't normally acknowledge.
Remember how all the important figures from his past pop up in the woods? Traveling through the woods is like traveling through the troubled subconscious of Hawthorne's main character. Hold on to your hats. (And maybe carry an axe.)