The title reflects on the famous wall at hand, and refers to the ritual that our speaker and his neighbor undergo every spring to fix this wall. That’s all well and good, but we have a few questions about this seemingly self-explanatory title, Mr. Frost. For example, why didn’t you call the poem "Mending the Wall" or "Wall Mending?" The title, "Mending Wall," makes us think that this wall is a supernatural thing with healing powers which magically mend any broken thing that you give it.
We also can’t help but think about the medical connotation at the heart of the word "mend," as in "I’m on the mend," or "my wound is mending well." The title also sounds to us like a short-hand message left on our speaker’s front door, explaining his whereabouts to people who happen to visit while he’s away (kind of like a "gone fishing" sign). Whatever the case may be, the title draws our attention to the star of the poem, the wall. Perhaps you’ve seen this wall in other hits, such as "Humpty Dumpty" and Wall-E… hehe. The –ing ending of "mending" makes us think that the mending process is in the works, and it gives the title a little momentum and movement (like the little round stones that keep falling out of the wall).