There is some fascinating neurological research being done by Andrew Newberg on the effects of religious thought on the wiring of the brain. What he has found is a great argument for the power of top down processing.
If you believe in a loving G-d, these thoughts build up the connections in your frontal lobes and anterior cingulate. This is where reason and empathy reside. So this belief can make you more rational and more empathic. But a belief in a vengeful G-d builds up connections in your limbic system where emotions like aggression and fear reside. So this belief can make you more aggressive and afraid. By building up connections in the brain, these effects can create positive reinforcement loops. Belief in a benevolent G-d makes you into the kind of person more likely to see good in things and people, strengthening these brain areas still further in a virtuous cycle. Belief in a vengeful G-d has the opposite effect in a vicious cycle.
These findings can easily be extrapolated beyond religion. People who have positive or negative beliefs about the external world in general probably experience similar neurological effects. In essence, it illustrates the power of positive or negative thinking in general. This is not some new age psychobabble. Our outlook on life can actually create the life that we want to some extent by wiring our brains to see it that way and guide our experiences to make it so.