In your opinion what causes christians to believe in Jesus

[Alan V]

I guess John is talking about temporary doubts, and believing as an act of will as the cure.  So suppression of doubts would be considered a virtue.

Yes; but it's not so much that suppressing doubt is a virtue. It might be analogous to the idea that courage isn't the absence of fear but the ability to fear and still move forward.

In this context I should mention that we atheists have far too much experience with unreasonable theists to think relatively reasonable theists are generally representative.  

Many of us did, after all, grow up within religious communities.

So that begs the question of whether religious ideas are generally helpful or harmful to people.