What is the significance of the forest in The Scarlet Letter?

Throughout the several chapters in which Hawthorne narrates Hester's encounter with Dimmesdale in the forest, he emphasizes that the forest is a place beyond the reach of law and the Puritan community that punishes Hester with the scarlet A.  At the beginning of Chapter XVI, "A Forest Walk," the text describes Hester's walk,

The road, after the two wayfarers had crossed from the peninsula to the mainland, was no other than a footpath.  It straggled...

Throughout the several chapters in which Hawthorne narrates Hester's encounter with Dimmesdale in the forest, he emphasizes that the forest is a place beyond the reach of law and the Puritan community that punishes Hester with the scarlet A.  At the beginning of Chapter XVI, "A Forest Walk," the text describes Hester's walk,

The road, after the two wayfarers had crossed from the peninsula to the mainland, was no other than a footpath.  It straggled onward into the mystery of the primeval forest.  This hemmed it in so narrowly, and stood so black and dense on either side, and disclosed such imperfect glimpses of the sky above that, to Hester's mind, it imaged not amiss the moral wilderness in which she had so long been wandering.

By describing the forest as "primeval," Hawthone indicates that its existence transcends history and thus stands apart from any given social organization including the Puritan community against which it stands.  Furthermore, the passage creates a symbolic connection between the "mystery of the primeval forest" with Hester's ambiance of "moral wilderness," making the forest a symbol of both Nature and the moral ambiguity that circulates throughout the book.  

In Chapter XVII, "The Pastor and his Parishioner," the novel underscores the forest's connection with Nature (as opposed to culture) in its description of scene of Hester and Dimmesdale's meeting:

It was no wonder that they thus questioned one another's actual and bodily existence, and even doubted their own.  So strangely did they meet, in the dim wood, that it was like their first encounter, in the world beyond the grave, of two spirits who had been intimately connected in their former life, but now stood coldly shuddering, in mutual dread;

The forest takes both characters beyond their historical "actual and bodily existence," turning them into something approximating "two spirits."  From these passages, we see that Hawthorne makes the forest a place symbolically outside of space and time, a space of lawlessness and moral ambiguity because of its untainted connection to Nature.