There seems to be an equivocation between "rational" and "believes only in things which are 'true.'" This is not at all what "rational" means:

[Rationality] refers to the conformity of one's beliefs with one's reasons for belief, or with one's actions with one's reasons for action... A rational decision is one that is not just reasoned, but is also optimal for achieving a goal or solving a problem. - http://en.wikipedia.org/wiki/Rationality

Suppose someone offered you a billion dollars to believe that the moon was made out of cheese. It would be perfectly rational for you to start believing in the cheese-moon hypothesis, assuming you valued the billion dollars more than you valued the 'truth'.

So what would it take for a rational agent to believe God wrote a book? Like everything else, the solution is large sums of money.

A harder question to answer would revolve around defining 'truth'. We might suggest that to assert "X is true" means something like "it is useful for one to believe X". We could point to an increased sense of community among believers, for example, as evidence that belief in a divine being is useful and therefore true. This is a (poorly phrased version of a) tack that James took.

Another example of a perfectly rational yet non-scientific believer would be the Knight of Faith. One of my favorie Kierkegaard lines:

Kierkegaard uses the story of a princess and a man who is madly in love with her, but circumstances are that the man will never be able to realize this love in this world ever... The knight of faith would say "I believe nevertheless that I shall get her, in virtue, that is, of the absurd, in virtue of the fact that with God all things are possible." This double movement is paradoxical because on the one hand it is humanly impossible that they would be together, but on the other hand the knight of faith is willing to believe that they will be together through divine possibility. [emphasis mine]

There seems to be an equivocation between "rational" and "believes only in things which are 'true.'" This is not at all what "rational" means:

[Rationality] refers to the conformity of one's beliefs with one's reasons for belief, or with one's actions with one's reasons for action... A rational decision is one that is not just reasoned, but is also optimal for achieving a goal or solving a problem. - http://en.wikipedia.org/wiki/Rationality

Suppose someone offered you a billion dollars to believe that the moon was made out of cheese. It would be perfectly rational for you to start believing in the cheese-moon hypothesis, assuming you valued the billion dollars more than you valued the 'truth'.

So what would it take for a rational agent to believe God wrote a book? Like everything else, the solution is large sums of money.

A harder question to answer would revolve around defining 'truth'. We might suggest that to assert "X is true" means something like "it is useful for one to believe X". We could point to an increased sense of community among believers, for example, as evidence that belief in a divine being is useful and therefore true. This is a (poorly phrased version of a) tack that James took.

And of course there's the nuclear option - denying the value of "truth". Consider the Knight of Faith. One of my favorie Kierkegaard lines:

Kierkegaard uses the story of a princess and a man who is madly in love with her, but circumstances are that the man will never be able to realize this love in this world ever... The knight of faith would say "I believe nevertheless that I shall get her, in virtue, that is, of the absurd, in virtue of the fact that with God all things are possible." This double movement is paradoxical because on the one hand it is humanly impossible that they would be together, but on the other hand the knight of faith is willing to believe that they will be together through divine possibility. [emphasis mine]