"Mending Wall" is considered to be one of Robert Frost's most famous poems and it was one of his first poems to become generally known. The wall in this poem is a symbol of the human relationship between the speaker and his neighbor. The neighbors have to meet every spring to mend the wall that has been worn by natural forces.
The wall is the expression of the emotional barrier that separates the speaker and his neighbor. In this situation the speaker wants to tear down this barrier while his neighbor wants to keep it up. It is ironic because though he does not want the fence up and he does not want to fix it, he reminds his neighbor every spring that they need to mend it. In lines 27 and again in line 45, the neighbor says, "Good fences make good neighbors." The speaker feels they do not.
This is evident in lines 30-31 when the speaker says, "Why do they make good neighbors? Isn't it where there are cows? But here there are no cows." He feels that wall isolates him or the person who has built it, holding them back from sharing their experiences and establishing intimacy with their neighbors. In line 33, the speaker wants to know what it was that he was "walling in or walling out", but he could not see what it was. This poem is written in iambic or blank verse. Frost makes an exception in the two lines where the neighbor says, "good fences make good neighbors". These lines are made to stand out because they contain an important message.
Some critics think that the wall symbolizes the space each one of us needs around us. The speaker does not seem to understand that and the neighbor does...