A simple definition of confirmation bias
A perfect example of confirmation bias is when theists such as creationists or early earth proponents set out to prove the truth about their beliefs. They start with the conclusion and always end up completing their "search" with the conclusion. This is called circular reasoning and no matter how you present it, in the end it is not how true research and scientific studies are conducted. Whenever you start with your answer as a fact then your research is going to be tainted by various factors and is therefore invalid.
Noted Christian apologist William Lane Craig puts what he calls the "witness of the Holy Spirit" before all beliefs based on argument and evidence. In other words for a man such as this there is no evidence that would be sufficient to convince him that his faith is false. As long as he has his subjective experiences of the Holy Spirit and the words of scripture he has blessed assurance that he is on the right path to truth. He has basically started with his conclusion.
Another thing that I think is relevant is that the Bible like all other so called holy or divinely inspired texts is entirely subject to human interpretation. Why is it that the gods don't speak clearly on important matters? Could it be because these texts were not the products of divine inspiration but in fact have quite human origins? The many scientific errors found in the Bible for example demonstrate that this book was written by men and possibly women in a less enlightened age. Christians try to explain this obvious fault in one of two ways: either the Bible is not meant to be a book about science, or God only revealed things that were important to the faith and salvation of the believers. Basically, the good Lord only gave the authors of the scriptures partial revelations of theological importance.
One of my favorite quotes on the divine inspiration of the Bible or any other so called divinely inspired text comes from the book 'The Age of Reason' by Thomas Paine. Speaking about the idea of a divine revelation he says:
"But admitting, for the sake of a case, that something has been revealed to a certain person, and not revealed to any other person, it is revelation to that person only. When he tells it to a second person, a second to a third, a third to a fourth, and so on, it ceases to be a revelation to all those persons. It is revelation to the first person only, and hearsay to every other, and consequently they are not obliged to believe it."
This is the most logical explanation for divine revelation that I have ever seen, and with all of the books I have read on Christianity and religious beliefs no one has said it better than Paine. Basically, what theists of all religions based on texts or even oral traditions are doing is basing their entire lives and belief systems on hearsay!
The reason that the various "divinely" inspired texts of the world are so contradictory is that they are subject to change due to several factors. The main one is translation into foreign languages that don't convey the same meaning as the original texts. Although even in the original texts most of these scriptures are internally contradictory. This leads us to the second and most damning reason of all: human interpretation.
According to a study conducted in 2011 by the Center for the Study of Global Christianity there are approximately 41,000 Christian denominations and organizations worldwide. Follow this link to read the 2 page article on this study here. Also, you can read more facts and statistics about Christianity here.
When you really think about it; instead of seeing them as 41,000 denominations view them as 41,000 individuals who started their own group within Christianity because of doctrinal differences due to interpretation of the scriptures. Every group claims to have the so called "truth" and considers other Christian groups as having strayed from the path or having been mislead because of incorrect exegesis of the texts. But even this fact is inconsistent with one of the promises Jesus is made to say in John 14:26 "But the Advocate, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you."
One of the jobs of the Holy Spirit was supposed to be to lead believers into all truth. Yet assuming Jesus died in 35ce at the latest, it has been 1,978 years and instead of the Spirit leading the church to all truth it seems that he has divided them! All 41,000 denominations claim to have the guidance of the Spirit and as such lay claim to the absolute truth of their chosen denominations doctrinal beliefs.
Mark 3:25 said it best: "If a house is divided against itself, that house cannot stand." Christianity's greatest war is the one that they wage against themselves.
Note: All biblical citations are from the New International Version.