We find out quickly why this story is called "Barn Burning." Abner Snopes is accused of burning down his landlord's barn. The landlord, Mr. Harris, tells the Justice of the Peace that Sarty, Abner's ten-year-old son knows the truth. Sarty's knows his father wants him to lie, and is terrified. Before he has to testify, the Justice and the landlord take pity on him. This initial tension between what Sarty wants and what his father wants drives the rest of the story.
We know Sarty planned to lie in court even though he didn't want to. Abner knows that Sarty wanted to tell the truth and assumes his son planned to betray him. Abner hits him and tells him that the most important thing in life is to "stick to your own blood" (29). Sarty feels powerless, and trapped. The scene with his father makes him realize just how much he wants to make his own choices. This stage extends the tension between father and son into a more distinct conflict.
When Sarty sees the de Spain mansion, he thinks it stands for "peace and dignity" (41). The mansion is hope for Sarty and he thinks its whiteness and opulence will soften his father and make him forget all about burning barns. The house means something entirely different to Abner. He knows that all such mansions were built, as he tells Sarty, from the "sweat" of black people, probably slaves. He shows exactly what he thinks of the de Spain fortune by deliberately tracking horse poop on the white carpet in the front room. The rug complicates things for Sarty. When de Spain isn't satisfied with the way the rug is cleaned, he belittles Abner in front of his son, adding extreme empathy for his father to the complicated emotions Sarty is feeling.
For all his empathy, Sarty has no intention of being an accomplice in the burning of another barn. After he alerts de Spain that the barn is about to be burned his life can never be the same again.
When Sarty is running, we aren't sure what will happen. We don't know if after warning de Spain he will try to warn his father that he warned de Spain, or what. In part because he's so young, we are very worried for him. The fact that he is a child and therefore vulnerable increases the suspense meter. Plus, we don't know for sure at this point if Sarty is a tragic hero, one who meets tragedy at the end of the story.
After all that running and frantic action, Sarty finally takes a breather. There is a definite sense that Sarty is at a middle point in his life. It's midnight, and he's on top of a hill, with his back to the past and his face to the future. The nightmare is behind him, and the unknown is before him. In this stage the action is inside Sarty's head and body, as he mourns his father, and sleeps to rejuvenate himself.
The story's last line makes it clear that Sarty is moving forward, away from his old life. In this sense, the story's conclusion is final. We don't know what will happen to him, but there is something exhilarating about the fact that even at ten years old, Sarty is determined to do things his way, to make his own choices, and live by his own code of honor.