For my part art the Gathering of Poets, I read a segment from the Preface to the 1855 edition of Leaves of Grass:
The American poets are to enclose old and new, for America is the race of races. Of them a bard is to be commensurate with a people. To him the other continents arrive as contributions . . . he gives them reception for their sake and his own sake. His spirit responds to his country's spirit . . . . he incarnates its geography and natural life and rivers and lakes. Mississippi with annual freshets and changing chutes, Missouri and Columbia and Ohio and Saint Lawrence with the falls and beautiful masculine Hudson, do not embouchure where they spend themselves more than they embouchure into him. The blue breadth over the inland sea of Virginia and Maryland and the sea off Massachusetts and Maine and over Manhattan bay and over Champlain and Erie and over Ontario and Huron and Michigan and Superior, and over the Texan and Mexican and Floridian and Cuban seas and over the seas off California and Oregon, is not tallied by the blue breadth of the waters below more than the breadth of above and below is tallied by him. When the long Atlantic coast stretches longer and the Pacific coast stretches longer he easily stretches with them north or south. He spans between them also from east to west and reflects what is between them. On him rise solid growths that offset the growths of pine and cedar and hemlock and liveoak and locust and chestnut and cypress and hickory and limetree and cottonwood and tuliptree and cactus and wildvine and tamarind and persimmon . . . .and tangles as tangled as any canebrake or swamp . . . . and forests coated with transparent ice and icicles hanging from the boughs and crackling in the wind . . . . and sides and peaks of mountains . . . . and pasturage sweet and free as savannah or upland or prairie . . . . To him enter the essences of the real things and past and present events---. . . . For such the expression of the American poet is to be transcendent and new. It is to be indirect and not direct or descriptive or epic. Its quality goes through these to much more. Let the age and wars of other nations be chanted and their eras and characters be illustrated and that finish the verse. Not so the great psalm of the republic. Here the theme is creative and has vista.
In my literature class this past semester, some of the students (not many; a couple or so) didn't much care for Walt.
"He's a know-it-all," one student said. "He thinks he's smarter than everyone else."
"Well, sure," I said. "He's a cosmos!"
This student also thought Thoreau was a know-it-all.
A couple of things to investigate:
Here's someone writing about the Preface
Here's Bruce Noll’s website