The speaker of the poem says so because he has experienced that ‘something’ is there that causes the cold ground under the wall to swell and burst. The ground bursts in a way that the boulders come spitting out from within to the outside automatically.

This ‘something’ is the unseen force of nature. According to the speaker, the nature breaks the wall because it does not like it to stay there.

Poet has said that something is there that doesn’t love a wall is that there is some elfs type creature that brings down the wall without anybody knowing that something happened but in metaphorical meaning of it is that the neighbor does not want the wall between them. The poet also adds that his apple orchards will not eat his pine cones but the neighbor doesn’t agree and said that  ‘good fences make good neighbors’.

The speaker says that they do not need the wall because their fields are of two different kinds. The neighbour’s field has pine trees whereas the speaker has an apple orchard. The speaker feels his apple trees will never get across and eat the cones under his pines, and vice versa

The poet says the above lines to refer to a natural power which is trying to destroy the wall. Later the poet also adds that the hunters are also destroying the wall to please their yelping dogs.

Something is there that doesn’t love a wall — in the beginning of the poem the narrator is referring to some supernatural Power that is the reason for the breaking of the wall.

When 2nd time it is used it refers to a supernatural Power or a creature that breaks the wall without anyone knowing and trying to convince the neighbour that there is no need of a wall.