We call it ‘Nature’; only reluctantly admitting ourselves to be ‘Nature’ too,” Denise Levertov wrote in her revelation of a poem “Sojourns in the Parallel World,” a generation after history’s most poetic piece of legislature termed that parallel world “wilderness” and defined it as “an area where the earth and its community of life are untrammeled by man, where man* himself is a visitor who does not remain. Those of us who visit wild places the way others see churches and concert halls visit because we return transfigured, recomposed, exalted, and humbled at the same time, enlarged and dissolved in something more significant at the same time. We stay because we undergo some essential self-composition in the poetry of existence, though its essence rarely lends itself to words.

That ineffable essence is what Henry David Thoreau (July 12, 1817–May 6, 1862) — who saw Nature as a form of prayer — articulated with uncommon clarity and splendor of sentiment in the final pages of Walden (public library | public domain), the record of the radical experiment in living he undertook a week before he turned twenty-eight.
We need the tonic of wildness — to wade sometimes in marshes where the bittern and the meadow-hen lurk and hear the booming of the snipe; to smell the whispering sedge where only some wilder and more solitary fowl builds her nest and the mink crawls with its belly close to the ground. At the same time that we are earnest to explore and learn all things, we require that all things be mysterious and unexplorable, that land and sea be infinitely wild, unsurveyed, and unfathomed by us because unfathomable.
A century before, Rachel Carson observed that because “our origins are of the earth… there is in us a deeply seated response to the natural universe, which is part of our humanity,” Thoreau adds:
We can never have enough of Nature. We need to witness our own limits transgressed, and some life pasturing freely where we never wander. We must be refreshed by the sight of inexhaustible vigor, vast Titanic features, the sea coast with its wrecks, the wilderness with its living and its decaying trees, the thunder cloud, and the rain which lasts three weeks and produces freshets.
We can never have enough of Nature because Nature is not something to have — it is something we are. Epochs after Thoreau, when we wade into the wilderness with our bodies and minds, with a walking stick or a poem, we witness more than our limits transgressed.
We witness our boundaries dissolved, in turn dissolving that most limited and damaging foundational falsehood upon which the whole of the consumerist-extractions complex is built: that the rest of the living world is a parallel world, a place to visit and mine for experiences and resources with which to adorn and enrich our separate human world.