Biblical inerrancy is the concept that the Bible is without errors of any kind in the original manuscripts. This is an essential doctrine in American evangelicalism.
As stated by The Gospel Coalition "The doctrine of the authority and inerrancy of Scripture is that, as a corollary of the inspiration of Scripture, the God-breathed Scriptures are wholly true in all things that they assert in the original autographs and therefore function with the authority of God’s own words."
In other words, when the 66 ancient books of the Bible, from Genesis to Revelation, were written down by humans over a span of (purportedly) 1600 years, God guided the process so that every word in every document was without error in the original "autographs", that is, the pages actually written by Isaiah, Paul, etc.
This was once my belief. I now see it to be, well, not even wrong, but meaningless - that is, it cannot be tested and it doesn't really tell us anything about the Bibles we have now. Instead, the belief in inerrancy serves as an article of faith, a boundary marker for identifying who is "faithful" to Scripture and who is not.
But here are some of the problems with it.
Inerrancy applies only to the original manuscripts (the 'autographs'). We are SO far from having the original manuscripts of any document in the Bible. In fact, with books like Genesis or the Gospels which show signs of being compiled from earlier stories, lists of sayings, and even orally-passed traditions, it is difficult to define what the "original manuscript" is.
The most recent manuscripts of New Testament documents are fragments, copies that were made starting in the early second century, with a few tiny fragments possibly from late in the first century. These, along with the many later copies, bear all the marks of human-copied material: Spelling errors, repeated lines, content inserted in the margin because the scribe maybe forgot it the first time. One of the things that makes the ancient Bible manuscripts so fascinating is to compare the ways they are different, and to note the things that seem to get added in or dropped as time passes.
One well known example of this is the famous story from John's gospel about Jesus and the adulterous women ("Let he who is without sin cast the first stone"). Nearly every modern English translation of John, even ones favored by evangelicals, acknowledges that this short story does not appear in the oldest sources, and that in some manuscripts it appears elsewhere in John, or even in Luke's gospel.
Whenever you see a footnote in your Bible that says "Some ancient sources say...", the translators are telling you that when you compare the ancient manuscripts, there is an alternate version of the text that appears in enough copies to mention. And in a Bible that contains such footnotes, you see them on practically every page.
Does this mean the Bible is riddled with errors? I don't think so. In comparison with other ancient works, the text of the Bible is very well-established. The vast majority of those footnotes I mentioned deal with small and fairly insignificant differences.
But to say that the original writings were without error tells us nothing about the Bible as we actually have it. Further, there is no evidence for this claim. It is asserted because belief in an inerrant Bible is a useful tool for telling people how to live and for accumulating power over others.
Most of us read the Bible in a language other than ancient Hebrew and Greek. If we DID have the original writings (we don't) and the experts could tell us with certainty, "Yes, these are without error" (a fantasy), that would be significant. But I couldn't read them. I need an English translation. And I'm in luck. There are dozens of them, many of them produced or updated in the 21st century.
Why are there dozens of them? Well, each one was produced because someone thought that the others didn't get it quite right.
When I was a kid, I thought that learning Spanish would involve nothing more than taking a sentence in American English and swapping out the words with Spanish ones. I later found out that the two languages have different ideas about sentence structure, the use of gender, verb tenses, pronunciation, etc., making it impossible to precisely translate a Spanish book to English. Compromises have to be made, and different translators make different choices about how to convey the original meaning in the receptor language. And Spanish and English are fairly closely-related.
Imagine the greater difficulty in translating an ancient language into modern English (which, by the way, is itself always changing). There is simply no perfect way to do it. Each English translation makes dozens of choices. How "literal" should we try to be? How much freedom do we have to rearrange an ancient sentence into something modern readers can understand? When the text says something about "all men" and we know it means "all people", can we say it that way or not?
Every translation team also makes choices that reflect a theological perspective - their own or that of their intended readers. The New International Version, for example, often smoothes out textual difficulties in a way that fits with the expectations of evangelical readers. The NRSV, the favorite Bible of mainline churches (and almost never seen among evangelicals) uses inclusive language almost to the point of distraction. And as you might imagine, these two Bibles differ in how they render verses that deal with same-sex relationships.
The point is that there is no one way to translate from Greek and Hebrew to English, so no two English translations are the same. And we've hardly mentioned the difficulty of translating from an ancient and very foreign culture to a modern one. This is, of course, all very obvious and normal. It's just that a theory about original manuscripts without errors has nothing to do with the Bibles we have.
Just because we all read the same words doesn't mean we all read the same thing. Even if we all read the same Bible (which we don't because of the above), we have a way of seeing different things in it. My father-in-law used to say that "we don't see things as they are, we see things as WE are". Nowhere is this more evident than in the number of Christian denominations across the world.
By some estimates, there are more than 45,000 Christian denominations, though this is a bit misleading because many churches from the same tradition are divided by country, language, etc. into official denominations. In the United States there are several hundred denominations. Each of the major branches of Christianity (Catholic, Orthodox, Protestant, etc.) was established (in part) because people disagreed about what God's plan was for ordering church and society.
Beginning with the Protestant Reformation around the 1500s, the Bible took center stage as the revelation of God's plan for our lives (not coincidentally because the printing press was invented at about the same time, so text-based authority became possible). From the start, Protestantism has been characterized by dividing, and sometime by ugly skirmishes and even wars, over differences in interpretation (Luther and Calvin, right out of the gate, came up with two very different ideas about Christianity based on their understanding of the Bible). Nearly all of those several hundred denominations in the U.S. are descendants of the Protestant Reformation.
When my parents started taking us to church, they chose a denomination where people believed that speaking in tongues and proclaiming prophetic messages were supposed to be part of worship, and every Sunday they did their best to prove it. After a few years, we started attending a church closer to home, where they believed that miraculous gifts like speaking in tongues and prophecy had definitely ceased when the last of Jesus' apostles died off, and that people today who did such things were either faking it or dabbling with demons. As a young adult, I took a middle position between the two, which made me a compromiser or a coward in the eyes of the stalwarts of my previous churches (though they were nice about it!)
The most important question in the Bible (according to many Protestants but by no means all) is: "What must I do to be 'saved'"? Being "saved" means (to many Protestants but by no means all) having your sins forgiven so you can go on living forever with God when you die. The Bible should provide a clear answer to that. And it does. In fact, it provides several.
I belonged to a religious group (we didn't like to be called a denomination) that took a minority view on this question. We found our clear answer in Acts 2:38 where it says to repent and be baptized for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. Our adherence to this verse made other Christians think of us as strange legalists. It wasn't the command to "repent", to turn away from our sins. Most (but by no means all) Christians think that salvation should involve repentance on our part. It was the command to be baptized (and by "baptism", we meant being dunked completely under water) that caused others to consider us weird.
Why didn't they see it like we did? Acts 2:38 couldn't be clearer.
But other verses are equally clear with a different message. John 3:16 is the most famous of them, where "whosoever believeth in him shall not perish but inherit everlasting life". No mention of baptism or even repentance here.
Christian belief about salvation spans a wide spectrum and Christians disagree about even the very basics, like: Do you have to make a "decision for Christ" or can you gradually grow into belief? Are people free to accept or reject God, or are they predestined from the foundation of the world to do one or the other? Is repentance part of being saved or a result of it? Can you lose your salvation? Is it an individual matter, or can a father decide for his whole family?
Each of these positions can be defended with teaching or examples from the New Testament...as long as you ignore other teachings and examples from the New Testament. This is, in fact, what Christianity in America looks like today.
Even if the original documents of Scripture were communicated from God to people without errors, how is that relevant to the Bible that we have, in which Christians can find dozens or hundreds of issues about which there are disagreements important enough to divide over?
Inerrancy is a boundary-marker, a fence to separate "us" from "them". It is backed by no evidence and it says nothing meaningful about the Bibles that we have or the different ways we read them.