The many, many descriptions of the scorched earth, distant sun, ashen drifts, cold weather, and endless rain all serve to paint a very bleak and hopeless existence, an existence that perhaps, is symbolic of life without the existence of good people who feel that they have communication with God. It emphasizes the world as it might be if humanity gets to the point where they are willing to nuke each other into oblivion. For the world to get to that point, they have to be pretty callous, godless men in the first place. The quote that accompanies your question ties directly into the symbolism of the barren land. McCarthy seems to be indicating that a land that has "no godspoke men" is a land not really worth living in, since all of the "godspoke men" left, taking with them any semblance of civility and "the world." There are not many kinds of men left. One is the group that has digressed to the point of feeding on each other's flesh. That is the worst kind of existence, the worst kind of man, just as the landscape is the worst kind of landscape, the worst kind of environment to live in. Any other "good guys" on the earth are in hiding, just like the narrator and his son. And, then, the other type of person left is the type of man that he is, one who even doubts the existence of a God. He often questions him, and is angry. He demands of God near the beginning of the story:
"Are you there? he whispered. Will I see you at the last? Have you a neck by which to throttle you? Have you a heart? Damn you eternally have you a soul?"
The barren landscape serves as a symbol of the souls of men who are left to exist there. They exist without any purpose, meaning, or belief system other than survival. When the "godspoke men" left the world, this is what was left. A world where men annhilate each other, then fight to survive.
I hope that those thoughts help; good luck!