"Circles in the Sand"

The white man drew a small circle in the sand
and told the red man, "This is what the Indian
knows," and drawing a big circle around the
small one, "This is what the white man knows."
The Indian took the stick and swept an immense
ring around both circles: "This is where the
white man and the red man know nothing."

a)This poem is not structured into lines and stanzas.
What kind of effect does the lack of structure have?
b)What does the white man mean by drawing the two different circles?
c) What point does the indian make through his answer?
d) What is the poet's message, in your opinion? Could you sum it up in your own words?