After the first read of this poem by Whitman, to me he is describing the mystery of the universe. To me he is describing the universal "Aum" that lives within and around us. We know it in different ways -- the unstruck note for instance. He calls it 'unheard by sharpest ear, unform'd in clearest eye.'
This reminds me of Guru Nanak's Aarti where he describes "Ek Omkaar" -
Several are your eyes, yet no one eye is yours
Several are your forms, yet no one form is yours
Several are your feet, not one foot without an essence (path)
You have several essences ... that's charming, amazing!
Here is Walt's poem:
A Riddle Song
By Walt Whitman
That which eludes this verse and any verse,
Unheard by sharpest ear, unform'd in clearest eye or cunningest mind,
Nor lore nor fame, nor happiness nor wealth,
And yet the pulse of every heart and life throughout the world incessantly,
Which you and I and all pursuing ever ever miss,
Open but still a secret, the real of the real, an illusion,
Costless, vouchsafed to each, yet never man the owner,
Which poets vainly seek to put in rhyme, historians in prose,
Which sculptor never chisel'd yet, nor painter painted,
Which vocalist never sung, nor orator nor actor ever utter'd,
Invoking here and now I challenge for my song.
Indifferently, 'mid public, private haunts, in solitude,
Behind the mountain and the wood,
Companion of the city's busiest streets, through the assemblage,
It and its radiations constantly glide.
In looks of fair unconscious babes,
Or strangely in the coffin'd dead,
Or show of breaking dawn or stars by night,
As some dissolving delicate film of dreams,
Hiding yet lingering.
Two little breaths of words comprising it,
Two words, yet all from first to last comprised in it.
How ardently for it!
How many ships have sail'd and sunk for it!
How many travelers started from their homes and neer return'd!
How much of genius boldly staked and lost for it!
What countless stores of beauty, love, ventur'd for it!
How all superbest deeds since Time began are traceable to it--and
shall be to the end!
How all heroic martyrdoms to it!
How, justified by it, the horrors, evils, battles of the earth!
How the bright fascinating lambent flames of it, in every age and
land, have drawn men's eyes,
Rich as a sunset on the Norway coast, the sky, the islands, and the cliffs,
Or midnight's silent glowing northern lights unreachable.
Haply God's riddle it, so vague and yet so certain,
The soul for it, and all the visible universe for it,
And heaven at last for it.