We know there is something, but we don't know what. The wall is a symbol of strength as we are told that it "spills the upper boulders" and "makes gaps even two can walk abreast". The forces that send out the "frozen ground-swell under it" are set on destroying it, yet these forces are never revealed. Frost uses the line twice in the poem to remind us that something somewhere does not like a wall.
The neighbors use the wall as a gathering place to meet and share an outdoor experience. They share the common nuisance of hunters that have damaged the wall. They struggle to mend the wall together and cooperate on locating it exactly on the property line. The difficulty they share is shown when Frost says, "We have to use a spell to make them balance: 'Stay where you are until our backs are turned!' We wear our fingers rough with handling them.". This common goal is "just another kind of outdoor game". Frost is sharing the outdoors and enjoying the wall.
While the neighbors are mending the wall, the wall is acting as a separation to the men. Frost says that "And on a day we meet to walk the line and set the wall between us once again. We keep the wall between us as we go. To each the boulders that have fallen to each". The wall has defined the space and dictated the realm of each man. ...Show more