How is the testing of faith a major theme in All the Pretty Horses by Cormac McCarthy?

Cormac McCarthy has said that each of his novels is a wrestling with the God problem.  While McCarthy, like John Grady, is an ethical, even religious man, he is too smart to reveal his hand in his novels.  He no doubt believes that the God problem is intensely personal and, as such, he would never divulge an ideology in his books.

In his latest book, The Road, McCarthy gives a few more details about his stance on God.  He says, "There is no God, and we are his prophets," a kind of paradoxical both-ways belief in non-belief.

In Chapter IV, Part I of All the Pretty Horses, Rawlins and Grady have frank discussions about belief and doubt in their quests.  John Grady has been raised a Christian, but just as he is coming-of-age as a man, he is coming-of-age as a believer too.  As such, he is open to doubt.

Rawlins is more forth-giving.  He thinks that God looks out for him:

Way the world is. Somebody can wake up and sneeze somewhere in Arkansas or some damn place and before you're done there's wars and ruination and all hell. You dont know what's goin to happen. I'd say He's just about got to. I dont believe we'd make it a day otherwisetening to the water drip in the woods. Bedrock, this. The cold and the silence. The ashes of the late world carried on the bleak and temporal winds to and fro in the void. Carried forth and scattered and carried forth again. Everything uncoupled from its shoring. Unsupported in the ashen air. Sustained by a breath, trembling and brief. If only my heart were stone.  (92)

Later, John Grady and Antonio discuss God in Chapter 2:

But there were two things they agreed upon wholly and that were never spoken and that was that God had put horses on earth to work cattle and that other than cattle there was no wealth proper to a man.

Here, God seems like a natural Prime Mover who puts all living things into a natural order.

Still later, in Chapter 4 Alphonsa says this to John Grady:

There is no one to tell us what might have been. We weep over the might have been, but there is no might have been. There never was. It is supposed to be true that those who do not know history are condemned to repeat it. I dont believe knowing can save us. What is constant in history is greed and foolishness and a love of blood and this is a thing that even God - who knows all that can be known - seems powerless to change.

So, there seems to a divide as to the power of God and the power of fate.  Alphonsa is both "devout and heretical" according to one critic.  She believes that God is all powerful and yet powerless in the face of passional human will, another paradox that shows the duality of belief and doubt.

In the end, faith and manhood are intertwined in the novel.  Whereas both seem easy to prove in childhood, they become problematic when one crosses the threshold into adulthood.  Whereas manhood is measured in blood and sweat, belief and faith may very well be measured in doubt and questioning.  It is all part of a quest: it is the search that matters.