What is the theme in No Country for Old Men by Cormac McCarthy?

The cost of life is the central theme to this novel. Llewelyn Moss is hunting antelope when he comes across the carnage in the desert. Closer investigation however reveals a drug deal gone bad where two sides accustomed to violence turned on each other, and in a bloody shootout, took each other out leaving the drugs and money in the desert. Llewelyn makes the decision to pack out the cash, even though he knows that whoever owns the money won't rest until they find it. It is a calculated gamble that will bring the criminals to his doorstep and into his life.