That's a good question. If you believe countless preachers, who claim they speak for god, than religious faith simply doesn't require any evidence, and no amount of argument or reason can sway the belief of someone who has the proper amount of faith. As to the question of where exactly this is addressed in the bible, there are a lot of scholars here who know the bible far better than the Christians who visit, perhaps one of them can provide the answer.
ETA: I see that this has been addressed.
Also, yet again, we see someone offering stories from the bible as evidence that the bible is true. It isn't evidence, it's circular.