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:

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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:

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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.