Told from the point of view of a brick wall, the poem is really about carrying a heavy, lonely responsibility. The wall stands "proud and strong," but it pays for that strength by being alone. An enemy keeps pounding it, helpers drift away too soon, and when it finally falls, chaos spills into the space behind it. Then someone repairs it, and the whole cycle starts again.
The speaker sounds tired, a little bitter, and still stubborn. It longs to step away "for a little bit," yet it can't, because the enemy would get in. It also insists that the enemy is wrong to think it has no feelings or strength, and hints that they will regret it someday. The wall seems to stand for anyone who takes the blows so others can feel safe, though the poem doesn't say exactly who the enemy is. The mood is weary and defiant, and it ends on a quiet note of hope: one caring person fixes the wall, and everyone is safe again.