Description and challenges of the poet by Whitman

In the 4th paragraph Whitman says: "The American poets are to enclose old and new for America is the race of races."
He challenges him by saying:" For such the expression of the American poet is to be transcendant and new."
"Of all nations the United States with veins full of poetical stuff most need poets and will doubtless have the greatest and use them the greatest."
"Their Presidents shall not be their common referee so much as their poets shall." 
"Of all mankind the great poet is the equable man."
With all these statements Whitman challenges the American poet.