Our Bible is a record of God's interaction with us, his created and beloved children. The various books were written a long time ago by people. They were devout, sincere servants of our just and loving God but they were people - just like us.
Our Bible contains a number of passages in which God is recorded as speaking directly to people; sometimes to individuals, sometimes to groups.
We know quite a bit about who wrote some of the New Testament texts and why. We know a lot less about most of the Old Testament and even less about the earliest books of the Old Testament. However we do know that all the writings that make up our Bible were written by people. We also know that people are, by their very nature, fallible. People make mistakes.
Copies of the original writings were made by people, and copies of those copies were made and so on. Eventually certain writings were considered to be important enough to be included in the various collections of writings used at different times by different denominations. The decisions as to which books should be included were, again, made by people. It was also people who translated those collections into different languages and gave us the various translations of our Bible that we use today.
Inevitably, because these copies were being made by people, changes crept in. Today we do not have any of the original writings. However we do have lots of copies, some of which are hundreds of years old. When scholars compare these copies they find that changes have been made over time. This is why, if you have a good study Bible, you will see footnotes that indicate that in some manuscripts a particular passage is missing or is worded differently. The story of the woman caught in the act of adultery is a good example. In our English Bibles the story is recorded in the first 11 verses of John 8. The footnotes let us know that scholars have not found the story in this place in the oldest available manuscripts of John’s gospel. It turns out that some ancient manuscripts have the story in another part of John while some have it as part of Luke’s gospel. This doesn’t mean that the incident didn’t happen - scholars are mostly in agreement that this is an authentic story of Jesus.
Because our Bible is the product of many, many centuries of copying, collecting, editing and translating, it has some contradictions and complexities. The important thing is that God speaks through it to us, today.