At the end of Chapter 12, Christmas gets out of the car that drove him partway out of town and realizes he is still holding the revolver he took from Joanna when he killed her. The unexploded chambers foreshadow the violent end of the novel:
The match burned down and went out, yet he still seemed to see the ancient thing with its two loaded chambers: the one upon which the hammer had already fallen and which had not exploded, and the other upon which no hammer had yet fallen but upon which a hammer had been planned to fall.
"Chekhov's gun" is a literary rule holding that no detail in a story should be extraneous. Eventually, even seemingly irrelevant details will turn out to be important. This rule is not hard and fast, but a classic example is that if a gun shows up early on in a story, it will go off by the end. The Civil War gun has not technically fired yet. It has one more loaded chamber that threatens to do so by the end of the novel.
The gun is an old Civil War revolver that can be loaded with two shots at once. Joanna had loaded both chambers. Although Faulkner is not explicit about what happened in Joanna's bedroom, it seems as though she planned to use one bullet on Christmas and the other on herself. When Christmas refused to pray, as she directed him, she pulled the trigger. However, when the hammer fell on the chamber, the gun failed to go off. The ammunition was a dud. Christmas then seized the razor he had previously set aside and killed Joanna, nearly cutting her head off. He then apparently took the gun and ran, although he is surprised to find that he has the gun.
There is an argument that Christmas was acting in self-defense. Then again, the intensity of the near-beheading combined with the fact that he brought the razor to begin with challenges this narrative. The real reason for Joanna's death is that the two had a tumultuous relationship, and neither was mentally well. The gun in Christmas's hand foreshadows that the nuance of the situation is soon to be lost. As a relic of the Civil War, the gun symbolizes the violence and White supremacy that still linger in Jefferson and in the rest of the South. They can't ever be rid of it. Just as Joanna and Christmas could not seem to stop themselves from picking up this old gun, the people of Jefferson will not be able to stop themselves from seeing Joe Christmas through the lens of deadly propaganda about Black men. He will be reduced to the stereotype of a violent Black man who had an affair with a White woman and killed her.
Faulkner suggests that by embroiling himself with Joanna and the family history that brought this gun into her possession, Christmas has essentially pointed the gun of White supremacy at himself. He spends the rest of the novel waiting for it to explode. Finally it does, and he suffers a horrific lynching that further reinforces Jefferson's fate as a place of racial terror.
In Chapter 15, a group of men in Mottstown brings Mr. Hines home after he recognizes Joe Christmas and calls for him to be lynched. The scene ends on a note of dramatic irony and foreshadowing when Mrs. Hines asks her husband about "Milly's baby":
Eupheus. You listen to me. You got to listen to me. I aint worried you before. In thirty years I aint worried you. But now I am going to. I am going to know and you got to tell me. What did you do with Milly’s baby?
True to the Gothic genre, Light in August features an orphan, Joe Christmas. Questions have swirled around Christmas's racial heritage his entire life. On the one hand, whether or not he is Black changes nothing about the actual events of the novel. On the other hand, much of Christmas's behavior is driven by the belief, by him and others, that he is Black and that his Blackness makes him violent. When Mrs. Hines asks Mr. Hines, "What did you do with Milly's baby?" the reader finally gets a partial clue as to who Christmas's parents are. Mrs. Hines is clearly also learning information she has been missing for 30 years, since Christmas was a baby.
Faulkner immediately cuts to a different scene, refusing to reveal everything right at this moment. The cliffhanger of a question not only amplifies the dramatic irony and suspense, but it also foreshadows the revelatory scene that usually takes place near the end of a Gothic novel. Soon, several of the characters will confess to one another all the information they have secretly been holding onto for years. By playing with the conventions of the literary genre he is using, Faulkner further highlights the fact that all of his characters are caught in a fictional story. They are all subject to tropes and patterns that were established long before they came along. Far from trivializing the novel as a representation of Southern culture, Faulkner's emphasis on its literariness helps the reader see how cultural stories direct the course of people's lives. Christmas's actual identity is in some senses less important than his and others' assumptions about who he is and what that means.
At the end of Chapter 17, Hightower goes to the planing mill and discovers that Byron has quit his job. Hightower believes that Byron has left town and that his role in the plot is done, but Faulkner foreshadows more drama to come for the minister:
‘So he departed without coming to tell me goodbye. After all he has done for me. Fetched to me. Ay; given, restored, to me. It would seem that this too was reserved for me. And this must be all.’
But it is not all. There is one thing more reserved for him.
For years, Hightower has cordoned himself off in his house, pessimistic about human nature and Jefferson's ability to overcome the sins of its past. He and Byron recently had a fight over Byron's request that the minister get involved in the town's affairs again by providing an alibi for Christmas. Before this fight was resolved, Byron asked Hightower to deliver Lena's baby. Delivering the baby made Hightower feel useful and connected to the future of the Jefferson community in a way he hasn't in a long time. He now thinks of Byron as someone who has passed in and out of his life, "restoring" him to a healthier version of himself. He contemplates the injustice of Christmas's impending execution, which his fight with Bryon prevented them from fully processing together. He accepts that "this too was reserved for me." It is not entirely clear what "this" is, but it seems as though he might mean the burden of knowing and failing to stop the tragedy of Christmas's execution. Byron has left him to bear this burden alone. Hightower sees the baby's birth and Christmas's death as the end of his own redemption arc: Byron has taught him again how to help his community where he can without being bogged down by its bad side.
Faulkner immediately lets the reader know that Hightower has misunderstood his own arc. He writes, "But it is not all. There is one thing more reserved for him." This ominous statement foreshadows the events of Chapter 19, when a mob lynches Christmas in Hightower's own house. Faulkner writes that this violent incident is "reserved" for Hightower: if Christmas is fated to die, Hightower is fated to host the racist mob in his own home. The lynching obliterates the idea that Hightower can keep the evils of his community at an arm's length. If he is going to be a part of Jefferson (which he inevitably is, whether he likes it or not), he must take it as it is. In the end, Faulkner leaves the reader with a portrait of Hightower as a man who is torn apart by the pain and incomprehensibility of his world.