There are several themes that can be seen in Gordimer’s short story.  I would examine the enotes essentials page on themes of the story. I think that there are several themes that can be taken.  One of which would be the idea that the more people strive for something that is “perfect,” the more seeds of personal destruction are planted.  The family in the short story are so concerned with crime and the external world that they build this fortress of a home, complete with alarms, protective gates, and barbed wire along with jagged edging on the exterior walls surrounding the home.  These elements are progressive steps taken in the hopes of ensuring that the outside world will not cause terror to the family.  They find that this ends up killing their child.  The example helps to bring out Gordimer’s idea that those who fail to fully understand and work with their existing reality and try to keep themselves insulated from it can end up concocting a cocktail of personal destruction as opposed to a state of created perfection.