We all believe different truths. Some us believe in absolute truth, others believe that there is no such thing and all truths are relative. What is true for one person is not true for another. The Bible teaches there is absolute truth, that is universally true, even if it is not universally accepted.
The question becomes, is the Bible actually true and can we trust the truths about Jesus and God that it proclaims.
In 1 John 1, John addresses this issue, stating that he was one of many eyewitnesses who personally witnessed the ministry of Jesus, and were convinced by His actions that he was the Son of God.