At the climax of the story, right before the officer submits himself to the torture device, he asks the explorer to read what the creator of the device wrote on the device's plans. The explorer is unable to read the words, as they look like nothing but "a maze of cris-crossing lines" to him. The officer then reads the words for him: "Be just" he says.
I think that this is the most significant moment in the entire story. I think that incomprehensible plans are symbolic of the paradoxical difficulty of being truly "just." It is this paradox that drives the officer to commit suicide upon the machine; he is tormented by the requirement to "be just" placed upon him by his mentor, the creator of the machine.
It is my opinion that the words to be engraved on the officer were "be just." The machine self-destructed because the officer was a part the machine itself. It destroyed itself as a symbol of the paradox of capital punishment- capital punishment is murder, which is a crime, which, in the penal colony's justice system, merits capital punishment. Murder is murder, however you slice it.
I think that the machine's creator is symbolic of man's most savage need for justice, even if it is really revenge. The officer and machine symbolize, as I've said, the paradox of capital punishment. The story's brutality serves as a starting point for a real-life discussion of crime and punishment.