The poem opens with a comment of the puzzled narrator about an unknown force that 'sends the frozen-ground-swell under it/And spills the upper boulders in the sun', producing measurable gaps in the wall. By the use of an unlikely compound noun: 'frozen-ground-swell', instead of a proper word, such as 'ice' or 'icicle', and the failure to relate the cracks as consequences of the former phenomenon the comment is likely to be the voice of a youth as well as a remark to the natural wonder.
Then the depiction of gaps caused by hunters disrupts the scene and brings in a preliminary conflict within the narrator's mind; that is, ironically, the narrator approves only of natural cracks in a wall not the man-made ones. He reasons that man-made gaps are forceful, destructive and merely for a personal purpose: 'To please the yelping dogs'. On the contrary, with the pausing effect of a Caesura as well as end stops and the use of words with long vowel sounds in a line followed closely by short vowel sounds in another:
'To please the yelping dogs. The gaps I mean, [short vowel sounds;
No one has seen them made or heard them made, long vowel sounds]
But at spring mending-time we find them there,'
the narrator expresses his wonder and admiration to a naturally-cracked wall. This preference foreshadows the narrator's calm but cold reaction on mending a wall at the end of the poem.
In line 11, 'But at spring mending-time we find them there', along with the rebirth of spring emerge gaps in a wall, coordinated reparation as well as a remarkable irony in 'mending wall', all of which prepare the ground for the central conflict of modern human relationship. Acknowledged of the mending time the narrator and his neighbor gather together in order to fulfill gaps in a wall. At this stage, the two characters are unified as the first person plural 'we', signifying the sense of unity and cooperation.
This is indeed an irony; the narrator and his neighbor become cooperative in order to be separate: '[...] we meet [...] and set the wall between us once again'. In addition, the description of the reparation is ornamented with quick, joyful but thoughtless rhythm, following from repetitive use of enjambment and childlike metaphor: 'Some [stones] are loaves and [...] balls'. Such playful words and rhythm characterize many childlike aspects of the narrator. He is initiative and enthusiastic: 'I let my neighbor know beyond the hill'; he is imaginative in a childlike way: 'Some are loaves and some so nearly balls/We have to use a spell to make them balance'. In fact, repairing a wall is a tough work:
'To each the boulders that have fallen to each. [unstressed ending]
... ... ... ...
We have to use a spell to make them balance: [unstressed ending]
"Stay where you are until our backs are turned!"
We wear our fingers rough with handling them.
Oh, just another kind of outdoor game',
hinted by such examples as the effect of interrupting uneasiness from continuous unstressed ending and some words, including 'have to', 'spell', and 'rough', that connote hardship. While mending the wall, the narrator is, however, overwhelmed thoughtlessly with joyful physical recreation and sense of collaboration with his neighbor. Even though he has remarked somewhere that the wall is set up again, the narrator seems ironically ignorant to the fact that 'mending wall' will later disunify his sense of 'we', the togetherness between himself and his neighbor. Once he realizes it an argument will be unavoidable.
At a particular point, 'One on a side' , Frost allows his narrator a pause for reasoning thoughts by applying a long-vowel sound followed immediately by a Caesura. The pause as well as the subsequent statement: 'It comes to little more', reports a wondering tone and suggests in some way that the narration is developing his intellectual maturity. He begins his first argument against the significance of 'mending wall', saying innocently 'My apple trees will never get across/And eat the cones under his pines'. He fails to argue his neighbor's murmur: "Good fences make good neighbors", though. Further on the main conflict of a revolutionary mind versus a conservative one has fully developed, illustrating Frost's concerned awareness of mental gaps in modern relationship. The unified 'we' has been split perpetually into two independent units: 'I' the revolutionary and 'He' the conservative.
No longer a pleasant wonder, the 'spring mending-time' has now become mischievous to the revolutionary mind. The narrator who once eagerly informed his neighbor of the mending-wall time would now prefer a world without borders and a neighborhood without 'fences'. The narrator, having passed the verge of maturity, bursts out a train of spicy, reasonable arguments made firm and effective by the use of rhetorical questions and enjambment:
"Why do they make good neighbors? Isn't it
Where there are cows? But here there are no cows
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 offense."
He views a 'wall' no longer as a springtime recreation nor a symbol of neighborliness and collaboration. It is a sign of 'offense', and he 'wants it down'. Nonetheless, the narrator only 'puts a notion [about the uselessness of a wall] in his [neighbor's] head' and refuses the use of force, even though he realizes that verbal encouragement may not work. The reason lies in his earlier detestation about the 'work of hunters'. That is, the narrator regards himself as 'apple orchard', polychromatic, fruitful trees of knowledge that make man civilized. Consequently, he would not degrade himself into the level of 'yelping dogs' just to 'have the rabbit(an intended metaphor for his neighbor) out of hiding'. He would rather have nature --as he could say "elves"-- take its course in destroying the wall.
The central conflict does not come as an overt interaction, and the narrator's treatment towards his neighbor is courteous in a sense. But, it is not on the whole, for his remarks about the neighbor are somewhat cold and contemptuous. The narrator likens his neighbor who dare not 'go behind his father's saying' to a gloomy, prickling pine tree with its inedible 'cones'. Then an image of an 'armed old-stone savage' is deployed to humiliate his incorrigible neighbor. Frost may be pointing out how a modern, revolutionary youth views conservatism in general, which is suggested as a step backward, a retreat into 'darkness'.
However, seeds of satire are also disseminated in the delineation of the rebelling narrator. The Fruit of Knowledge, which is compared to the revolutionary mind, is not only the cause of human intelligence but also that of human banishment from the Garden of Eden. Considering himself as civilized and assuming allegedly that his belief is unarguably correct, the narrator of the 'Mending Wall' is somehow driven by pride when he ridicules his neighbor as a prehistoric savage. Moreover, such premises as the eating of 'cones', the wandering of 'cows' and the uselessness of a 'wall' have their implication of materialism (Note that they are all materials and involve the gain/loss of benefits). Frost may intend to insert these defaults to make his subversive narrator less reliable and leave space for individual readers to judge according to their own favour.
When finishing 'Mending Wall' it is possible to assert that the poem is a microcosm of our changing world in which ones are gradually separated from the others as a result of ones' own bias, causing interminable gaps in human relationship. Portrayed in 'Mending Wall' are the narrator, the revolutionary mind, who assumes arrogantly his superiority to others and his neighbor, the conservative mind, who possesses indestructible sense of stubbornness. Frost has implied that the roots of all trouble indeed lie within these two egocentric characters. The wall itself stands as an ironic symbol of integration or reconciliation and does not account for the disintegration between the narrator and his neighbor.