Evil as a force, not a motive
Chigurh does not kill for money or revenge. He kills because his logic demands it. McCarthy presents evil as something that operates on its own terms, indifferent to human moral categories. Bell cannot fight it because he cannot understand it.
The failure of law and order
Bell is a good man and a capable sheriff, and he accomplishes almost nothing. The novel shows law enforcement as a system built for a world that no longer exists. Bell's retirement is not a choice so much as an admission.
Fate and the illusion of choice
The coin flip scenes make Chigurh's worldview explicit: the coin has been traveling toward this moment since it was minted. McCarthy tests that idea against every character. Moss chooses, Carla Jean refuses, Bell reflects, and none of it changes the outcome.
The cost of greed and conscience
Moss takes the money out of something like ambition. He goes back to the crime scene out of something like conscience. Both decisions destroy him. The novel does not reward greed or punish it cleanly; it just shows what the choice costs.
Time, age, and being left behind
Bell's narration is full of grief for a world he understood. He feels that the violence he is seeing is new and worse, though his uncle Ellis pushes back on that. The novel treats aging as a kind of exile from the present, and Bell's dreams suggest he is looking backward even as he tries to move forward.