I suppose you are refering to the way in which there is a gap between what any observer of what happens in this story could see and then the reality of what is really going on in the minds of these two characters. On the surface, this story represents a normal everyday event, one man doing his job and offering his services, and another taking advantage of that to get a shave. However, the narration of this brilliant story, and in particular the way in which the first person point of view gives us access to the thoughts of the barber gives this story a completely different and much deeper significance.
This narration allows us to know that the barber that is just about to shave the throat of Captain Torres with a very sharp razor is actually a member of the rebels that Captain Torres is trying to eradicate with such cruelty. This gives the story a new twist, as the barber is shown to contemplate how easy it would be to kill Captain Torres:
I could cut this throat just so--zip, zip! I wouldn't give him time to resist and since he has his eyes closed he wouldn't see the glistening blade or my glistening eyes.
Such ruminations add massively to the impact of this story as the barber has to choose between becoming a murderer or letting Captain Torres, his enemy, free. Of course, the story is made even deeper by the revelation at the end that Captain Torres knew all alogn that the barber worked for the rebels.