John 19:35 And he who has seen has testified, and his testimony is true; and he knows that he is telling the truth, so that you may believe.
John wrote these words that we now have in our bibles because he was an eye-witness to what was happening. He wrote it down because he knew it to be the truth.
When we have eye-witness accounts in a court of law we believe what has happened because we trust someone who is willing to come forward and speak the truth as it happened.
Why then do we have any doubts about God’s Word being the truth? Why should we not believe people who have seen it when all we are faced with theories from the other side?