What are some main points that I need to be sure that I include when writing an essay on inner conflict in "Barn Burning"?
I would want to make sure that you focus on how, even after Sarty has betrayed his father by informing on him to Major de Spain, he still struggles with his feelings for his father, trying to remind himself of how his father fought in the civil war and was a good man. That this conflict continues even after Sarty has crossed the boundary and chosen to betray his father shows how deep-seated this internal conflict is. This is of course brilliantly shown to us by the use of third person limited point of view which gives us access to Sarty's thoughts and feelings. His confusion about his actions gives testament to the massive conflict he is experiencing.
There's much to choose from when dealing with points to include concerning inner conflict in Faulkner's "Barn Burning." I don't know if the following are points you "need" to include, but they are points you could include.
Point of view is essential in revealing inner conflict. The story is told from the boy's point of view, though he is not the narrator. His inner conflicts are the ones revealed.
One way the narrator reveals Sarty's inner conflict is by relating his thoughts in italics. For example, in the opening paragraph, Faulkner writes:
He could not see the table where the Justice sat and before which his father and his father's enemy (our enemy he thought in that despair; ourn! mine and his both! He's my father!) stood, but he could hear them, the two of them that is, because his father had said no word yet:...
The central conflict is, thus, revealed through Sarty's thoughts: loyalty to his father and family (to his blood) vs. loyalty to what's right, to justice. In the opening paragraph, Sarty catches himself not identifying with his father, not thinking of himself as being on the same side as his father. This is essentially the conflict.
Inner conflict, then, is revealed through point of view and character thoughts, and that inner conflict is the tension between what Sarty knows is right and just behavior, and his father's behavior.