The main point of this story is that one reaps what one sows. The story can be taken as an allegory, representing how, in this modern era, we burn fossil fuels (and in the process pollute the atmosphere with billions of tons of carbon dioxide every year), shove garbage into landfills, pump sewage into the oceans, fire more rubbish into space, and we do all of this seemingly regardless of the damage we are doing to our planet and the consequences that future generations will suffer. We continue to produce and build, thinking only of the present and sparing hardly a thought for the future.
The twist, at the end of the story, when a small pebble falls past a construction worker, links back to the beginning of the story, when one of the villagers throws a pebble into the hole to see if he can hear it hitting the bottom. When the villagers realize that the hole seems to be endless, they decide to throw into it everything that they don't want—rubbish, corpses, nuclear waste. And meanwhile, "Aiming at the heavens, new buildings (go) on being constructed, one after the other," and the villagers assume that all of this production comes at no cost, because all of the waste products are being thrown into the seemingly bottomless hole. When the same pebble falls at the end, ironically past a construction worker, the reader realizes that all of the production does have a cost after all. The villagers will reap what they sow, and all of the waste that they threw into the hole shall soon come back to them.
This is a very neat, clever allegory to represent the modern world. We too surge ahead with endless production, with skyscrapers that reach to the sky and more and more cars for our roads, without thinking about how all of this production is polluting and damaging the earth. We think only of the immediate present, and behave as if there will be no consequences to face in the future.