The image of the trap setter
Cormac McCarthy is an image writer, meaning that his approach to prose is to provide snapshots of the scene and then to analyze the meaning. The first of these is the image that represents Billy's relationship to his father. What does it mean to follow his father's example? It means finding non-violent solutions to problems and being in control of his emotions. He gains this wisdom by staring at his dad setting a trap.
Boyd and his gunfights
It's the West. Some gunfights are unavoidable. But for Boyd, the gunfights are merely the manifestation of his willingness to be violent. Strangers pick up on this unsettling quality and twice in the novel, he is shot for saying the wrong thing to the wrong person. This image represents the quality of respect. What Boyd lacks in wisdom, he makes up for by acting impulsively, and the universe's way of saying no to that kind of behavior is to let Boyd get shot once—a hard lesson to learn, no doubt—and then when Boyd fails to learn his lesson, he gets shot and dies. There's a pretty clear moral insight from this image.
Violent imagery
McCarthy is known for his portrayal of violent imagery. Although this novel is perhaps less gory than most, it still includes violence as a theme, and the depictions of violence are brutal to be sure. The main depiction of violence is when Billy exhumes his brother from the grave and it attacked randomly by bandits.
Dark imagery, death imagery
Billy is learning about life and what he needs in order to survive his life as an adult. This means that he will have to understand death very clearly, and he does. He often comments wisely about his brother's morality and the risk of being angry. He sees Mexican bandits who try to kill him. He must exhume bones from the earth. Also, the implication in the last scene is that since he refused to help the dog, the dog will die. This understanding is ultimately the climax of the novel and also it's ending point. The boy, once he falls prey to his own anger and moral compromise, finally understands where evil originates—from suffering.
