Whenever I raise this question, someone will draw my attention to the first half of 2 Timothy 3:16 which is usually translated “All scripture is inspired by God”. Let’s look at this passage. Paul is writing a personal letter to Timothy who has been his companion and fellow worker for years. One respected commentator tells us that Timothy was “perhaps the most prominent, trusted and longstanding of Paul’s fellow workers” and refers to 2 Timothy as “the most personal (of Paul’s letters) written to prepare Timothy to carry on the work of ministry after Paul’s impending death”. So, we can expect that Paul would have taken great care in writing this letter. He would have wanted to make sure that he was getting across his message to Timothy as explicitly as he could.
To get the context of 2 Timothy 3:16, let’s start reading at verse 15: “from infancy you have known the Holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus.” What are these Holy Scriptures that our brother Paul is writing about? We don’t know, Paul doesn’t say, but if Timothy has known them from his infancy they must be found in the Old Testament because the decisions about which books were going to be included in the New Testament wouldn’t be made until hundreds of years after Paul wrote this letter.
The Greek word that is translated “scripture” in verse 16 means “writing” in Greek. The decision to translate it as “scripture” is entirely a decision made by the translators and publishers of modern English Bibles. Also, if you have a good study Bible (and it’s worth getting one) you will see that there is a footnote to the verse which shows that the Greek can be translated as “Every scripture inspired by God is also…”. So Paul’s words to Timothy in this verse may have been:
All scripture is inspired by God and is useful…
Or Paul’s words may have been
All scripture that is inspired by God is also useful…
Which translation best reflects Paul’s original meaning? We don’t know, but there can be no doubt about his explanation of what these writings should be used for. He tells Timothy that the writings he is talking about are “useful”. Useful for what? “…useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work” (2 Timothy 3:16-17). So, Paul is telling Timothy that these writings are “useful” for these purposes. Please note that he does not say that they are “essential”, nor even “important”. He says they are “useful”.
There is nothing in this passage to suggest that our Bibles are free from error or contradiction. This passage is often used to support the view that the whole Bible is inspired by God. But the passage itself clearly does not say that.
Here’s an important question: Can we be certain that Paul’s letters were inspired by God? When this question is asked someone is likely to quote this verse from 2 Peter:
“Bear in mind that our Lord’s patience means salvation, just as our dear brother Paul also wrote you with the wisdom that God gave him. He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other scriptures, to their own destruction.” (2 Peter 3:15-16)
There are two important points to make about this passage from 2 Peter:
Before we can accept that Peter was authenticating Paul’s letters as inspired by God, we have to be sure that Peter’s words were inspired by God. So, let’s talk about Peter. Peter was a human being (Acts 10:25-26). Nothing more than a human being. Nothing less than a human being. Peter is consistently portrayed in the New Testament as a human being who made mistakes and got things wrong sometimes (Some examples: Matthew 14:30-31; 16:22-23; 18:21-22; Mark 14:37; Luke 9:33; 22:33-34; 22:54-62; John 13:8; 18:10-11; 18:17; 18:25-27; Galatians 2:14). Yes, Peter was chosen by Jesus and experienced God speaking to him directly (Matthew 16:17; 17:4-5) but he was still, without question, and throughout his whole life, a human being who made mistakes and got things wrong sometimes. All human beings make mistakes and get things wrong sometimes. So, can we be certain that Peter, while he was writing his letters, did not make any mistakes or get anything wrong? What evidence is there that God guided every word that Peter wrote in his letters when God clearly did not guide every word that Peter spoke?
Secondly, Peter wrote: “our dear brother Paul also wrote you with the wisdom that God gave him. (2 Peter 3:15). Peter was not saying that God inspired Paul’s writings or that those writings were free from error or contradiction, but that Paul wrote them with the wisdom God gave him.
 David DeSilva, An Introduction to the New Testament, IVP Academic, 2004. P733.