As an atheist one of the most common questions I encounter from other atheists is the one about how theists can so firmly believe in the obviously false teachings of Christianity. Author and former pastor John W. Loftus put forth a challenge to theists called the OTF or the outsider test for faith. The challenge asks believers to critically analyze their beliefs with the same criteria that they use to invalidate all other religious beliefs. John Loftus has written a book on this issue but he also does a damn good job at explaining this on his blog Debunking Christianity.
I find his challenge to be more than reasonable but theists have complained that it is unfair. It is not a difficult challenge nor is it hard to understand, but if you read some of the complaints from theists you would think that they don't understand it at all. When I read about it for the first time I thought to myself that this is the exact process I went through on a mental as well as an emotional level when I finally broke free from Christianity's hold on my life.
One thing I know for sure is that faith is blind and as such is not persuaded by reason alone. True Christian believers who are fully invested in their faith are the hardest to convince since they are invested mentally and emotionally to the fullest extent possible. I was deeply entrenched in the faith and Christianity was my world at one time. It was all I knew and lived for. But the day I read the bible from cover to cover critically I was able to see the lies exposed in the source itself.
The more I read the bible the more questions I had about my faith. The kicker for me came after I had waded through the rivers of blood and mass murder in the bible leading up to Exodus 20 and the ten commandments. In those commandments it is said that God said thou shall not kill; but this led me to ask myself; then what the hell does God call all those murders he perpetrated? The only thing that makes sin sin is that it is offensive to God. But a careful reading of the scriptures would lead one to believe that sin is what God says it is when he says it is. Apparently, those commandments don't apply to him and when you kill in his name as the Hebrews apparently did several times throughout the scriptures its not a sin, because God commanded it at the time.
There are two key concepts in psychology that help clarify why theists have such a hard time seeing reason, especially when it comes to their faith. The first one I would like to discuss is known as compartmentalization. Wikipedia defines it as such:
Compartmentalization is an unconscious psychological defense mechanism used to avoid cognitive dissonance,
or the mental discomfort and anxiety caused by a person's having
conflicting values, cognitions, emotions, beliefs, etc. within
Compartmentalization allows these conflicting ideas to co-exist by
inhibiting direct or explicit acknowledgement and interaction between
separate compartmentalized self states.
This unconscious process makes it possible for an otherwise intelligent person to accept illogical and unreasonable beliefs. Mentally theists separate their faith from any an all ideas that may conflict or challenge it. There are actually scientists who do this on a daily basis when they are working in a lab where they are accustomed to analyze and question everything, but outside of the lab they never think to question their faith as thoroughly as they do other ideas or matters. That is why faith is the cornerstone of Christianity. It doesn't require evidence it just requires that you commit to believing it without evidence. Hence the term blind faith is quite fitting here.
The next key component in psychology that also works hand in hand with compartmentalization is known as confirmation bias. This concept helps theists maintain their faith because it allows them to only accept only "evidence" which seems to confirm what they already believe and discard contradictory ideas.
A confirmation bias is a type of cognitive bias
in which people tend to seek out information which agrees with
previously held beliefs. They also lend more weight to informational
input which supports their beliefs, while discarding contradictory
It is because of confirmation bias that theists can't be swayed by evidence that may contradict what they believe. They purposely look past the many contradictions in the bible and the many faults of their God. Despite the facts presented by evolution they still believe in having been created by some invisible guy in the sky. They can't see how ridiculous the tales of the bible are and outright impossible at times. There is nothing crazy about them literally waiting for a man that supposedly lived and died around two thousand years ago. Depite the facts, they still longingly await his so called triumphant return to earth to take them away to their eternal state of bliss in the imaginary utopia spoken of in the bible.
So there you have it, they are not dumb they are just blinded by the delusion of their choice. It's not about intelligence its about faith Religion has evolved along with every scientific discovery to the contrary. When you pick apart one aspect of their faith they just simply look for other irrational reasons to continue to believe the unbelievable.