We meet the officer as he's preparing the apparatus and describing it to the explorer, shortly before an execution. He's quite excited, and doesn't seem to notice that the explorer isn't.
The officer tells of how the apparatus and the colony were built by the old Commandant, and describes the basic parts of the apparatus.
The officer tells the now-more-interested explorer how justice works in the colony: no trial, no defense, automatic guilt. He's the judge of the colony, and sticks up for the way the old Commandant did things.
The officer continues to describe the apparatus and the process by which it writes on the body of the condemned man, though he's interrupted for a moment when he has to wake up the soldier and order him to hold the condemned man back from the machine.
Describing the twelve-hour execution process, the officer speaks of the moment of "enlightenment" that happens in the sixth hour, and says it's enough to tempt one to go under the apparatus oneself (hint hint).
Finished with his explanation, the officer orders the condemned man put into the machine. As he himself puts the gag on him, the man vomits and the officer is disgusted.
As the final preparations are being made for the condemned man, the officer makes his appeal to the explorer, telling him that he is the sole advocate the procedure has left in the colony and that it is under attack by the new Commandant.
After arguing with the explorer about whether or not he will be able to influence the procedure's fate, the officer demands help from the explorer, confident – or maybe certain – that he will help him.
When the explorer refuses, the officer is silent for a moment, and then announces that "The time has come."
The officer shows the explorer that his sentence shall be "BE JUST!" and then strips naked and enters the machine.
The machine falls apart, killing the officer in the most bloody possible way in a matter of minutes and denying him the "exquisite torture" he wanted.