There are people who have an appetite for grief; pleasure is not strong enough and they crave pain. They have mithridatic stomachs which must be fed on poisoned bread, natures so doomed that no prosperity can sooth their ragged and dishevelled desolation.
The poem is a little myth of man's capacity of making his life meaningful. And in the end, the poem is not a thing we see - it is, rather, a light by which we may see - and what we see is life.
When I would recreate myself, I seek the darkest wood, the thickest and most interminable, and to the citizen, most dismal swamp. I enter a swamp as a sacred place - a sanctum sanctorum. There is the strength, the marrow of Nature.