How does the speaker's repetition of the neighbor's cherished belief about the importance of walls (lines 27 and 45) convey the poem's criticism of an undesirable social pattern?

30 a town is built on the banks of a small lake on the edge of a desert. after some time, the townspeople discover that water from the lake has become too polluted to use. describe one way that the lake may have been contaminated by the actions of the townspeople, and explain how the townspeople can remediate this problem.