In your opinion what causes christians to believe in Jesus

[Sheldon]

However, that story can't be a "predictive mental model" (as he claimed) unless it also has roots in the real world.

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People believe in Christianity, not "for the same reasons anybody believes anything" as John claimed, but because they reject the evidence against the Christian story.

Of course all of this is obvious to atheists who prioritize evidence, just not to Christians like John. 

The brain doesn't care about representing the truth of reality, 

You really need to learn to avoid absolute claims, we clearly couldn't function without forming beliefs about the world, and though the utility of those beliefs needn't necessarily require that they always be true of course any individual can care about the truth of a claim. If they care to try and eliminate as much subjective bias as is possible, it's a huge scale from entirely subjective to objective facts, with the latter being the most reliable reflection of reality we have. This is without a doubt why humans have created methods that help achieve this, by adhering to strict principles of validation, like logic, and now science. 

it cares about functioning in it. And all of your beliefs serve a function, whether it is instrumental, symbolic, social, and so on.

We are our brain, obviously, and can choose to set as high, or conversely low, a standard for credulity as we wish, that is axiomatic. That we have evolved to think irrationally, and reason poorly, doesn't mean we have no other choice, again this is axiomatically true. gain I would have thought any psychologist worthy of the name would understand that. 

Now, regarding evidence: Evidence doesn't exist in a one-to-one relationship with truth.

What a spectacularly stupid claim. 

It never points to a single definite conclusion.

Two for two. 

Instead, it points in all directions, and can support multiple overlapping theories. It requires argumentation and interpretation to make a case for one exclusive view.

It can, though this is not always the case, and of course we have plenty of irrefutable definitive truths about reality, that are supported by an overwhelming amount of objective evidence. this is the same tired old canard I have seen creationist and religious apologists trot out, that because beliefs are all subjectively influenced, this makes them equally subjective, and thus an entirely subjective religious belief, is claimed to be as reliable as objective scientific facts, it's nonsense. 

If anyone is inclined to believe that a particular unevidenced archaic superstition is true, then they can,  and as long as they don't try and tell me I have to believe it, or live my life in any way as if it true, then they can fill their boots, but to claim it is as reliable a reflection of reality as objective facts supported by overwhelming objective evidence is clearly nonsense.