Both the speaker and the neighbor agree on the benefit of the wall. They both spend time repairing it. More than that, they repair it together.
The speaker, however, does question why exactly "Good fences make good neighbors." He does this, he says, more out of "mischief" than serious disagreement. He just wants to hear his neighbor's reasoning on the subject. But his neighbor doesn't provide him with his reasoning, he just repeats the saying of his father. It could be said that he is a traditionalist or conservative. Boundaries exist because boundaries have worked in the past.
1. Frost, the poet speaker, is the observant and enlightened neighbor. Every spring he realises that both nature (the melting snow) and man (the hunters) together make gaps in the wall. A combination of logical reasoning (apple trees grow in his plot of land and pine trees in his neighbor's) and intuition ("Something there is that doesn't love a wall") convince him of the futility of this annual ritual of trying to 'mend' this particular wall. But at the same time he is a perceptive person who knows when to build and when not to build a wall:"But here there are no cows...to give offence."
2. His neighbor, in direct contrast, is a conservative who will not listen to reason and is ofcourse completely immune to any sudden flash of intuition. All that he can do is merely repeat parrot like "Good fences make good neighbors." He is a prisoner of dogmatic traditionalism whose thought process and actions are bound in chains by the cliched formulas of his forefathers. Consequently, Frost is unable to convince him of the futility of 'mending' the wall. Frost very aptly sums up his character by comparing him to "an old stone- savage armed/ He moves in darkness as it seems to me." 'Darkness' ofcourse refers to his ignorance, his inability to see reason or receive wisdom and enlightenment intuitively.