Explain motivation behind the neighbor’s duties toward the wall and his favorite saying, “Good fences make good neighbors.” "Mending Wall"...

The neighbor desires property separation. He believes in
boundaries. Walls protect. Clearly, the neighbor is old-fashioned. He believes "good
fences make good neighbors." The significance of this phrase is that neighbors should
desire to be good one to the other, and if good fences help this process, then build a
good fence.

While the speaker of the poem would tend to not
see the necessity of the wall, he humors his neighbor. He restores the broken down wall.
Hunters and animals have broken down the wall. Restoring the wall is a good time to
fellowship and spend time with his neighbor.

Clearly, the
neighbor is motivated by tradition. His father taught him that "good fences make good
neighbors."

He
will not go behind his father's saying, 
And he likes having thought of it so
well 
He says again, 'Good fences make good
neighbors.'

Truly, the
neighbor is motivated by old-fashioned ideas. The speaker considers him old
fashioned:

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Bringing a stone grasped firmly by the
top 
In each hand, like an old-stone savage armed. 
He moves in
darkness as it seems to
me~

No doubt, the neighbor
may only believe "good fences make good neighbors" because his father taught him that it
was so. Some people hold on to traditions for sentimental reasons only. Clearly, the
speaker of the poem does not see the necessity of the wall. He even mentions that one
should really consider what one is walling out by building a
wall:

Before I
built a wall I'd ask to know 
What I was walling in or walling
out, 
And to whom I was like to give
offence.

The neighbor is set
in his thinking. He will not change his mind. Obviously, the speaker has ask him about
the importance of building a wall. To this, the neighbor repeats his
thoughts:

He
says again, "Good fences make good
neighbors."

This is just the
way the old-fashioned neighbor thinks. He learned it from his
father.