There is an easy, Sunday school answer to this. Jesus is the truth. At times truth and Jesus are used interchangeably, especially in John’s gospel. For example, John 8:32, ‘you will know the truth and the truth will set you free.’ Really it is Jesus that sets us free.
Jesus taught truth in a serious of stories and through his actions. The formal church then turned this into a set of propositional truths. This became a list of things to believe. This made it is easy to know who was ‘in’ and who was ‘out’. If you could tick all the things on the list you were in.
Jesus didn’t do this. Jesus was just there. He gave truth through his actions. When people were with Jesus, they ‘knew the truth’. Knowing Jesus doesn’t mean knowing a set of propositions. It is about knowing the person of Jesus.
The apostles were those who witnessed the resurrection. They had personal experiential knowledge of the risen Jesus. They ‘knew’ (in the Hebrew understanding of the word) Jesus. They wanted others to ‘know’ Jesus.
This idea is under attack today. People, continuing in hundreds of years of church history, want to reduce knowing Jesus to a series of propositional truths. This makes it easy to know who is ‘in’ and who is ‘out’. However this is not what the apostles taught, or even what Jesus taught.
Barth taught that revelation was something we encountered; it wasn’t a series of propositional truths. Whatever that might exactly mean, it is closer to the experience of the apostles.
What is truth? Truth is having experiential knowledge through a personal relationship with the Jesus, who is revealed in the Bible. Our experience of truth must align with the accepted teaching of the person of Jesus.
Many ‘Christians leaders’ are uncomfortable with staying with just this. This is because it is hard to define who is ‘with them’ or ‘in’ and who isn’t ‘with them’ or ‘out’ based on this. It is much easier to have a set of statements to which we must agree to determine who is in or out. So how do we determine who is ‘in’ and who is ‘out’?