What is the symbolism of the forest?
In early American Literature, the forest is the home of the strange and threatening (Indians) and is also viewed as the home of the devil (there was probably some relationship to the Indians in their minds). It was the perfect setting for the trip that Brown (may) have made that night.
For a good comparison with the use of the forest, read "The Devil and Tom Walker."
The forest setting and the path become increasingly symbolic with details such as " the dark wall of forest, an altar like rock, blazing pines, the strange sinful hymn with all of this bathed in red light. It would seem to be Brown's preoccupation with sin.
The woods are the physical location in which Brown explores his doubts and opposing desires, and as such represent his personal hell. Although Brown eventually leaves the physical location of the woods, mentally he stays there for the rest of his life.
The forest is symbolic of evil and things we do not know or understand. The forest is where anything can happen, including meeting with the Devil!