At the time it was written, the Bible was widely circulated and viewed by eyewitnesses to the events it records. As regards the New Testament, fragments of 5 books have been found from within 35 years of Jesus’ death. These eyewitnesses would have been in a position to refute what the authors had written and the lack of any such refutation provides further evidence for the reliability of the Bible.
In his letter to the church in Corinth, Paul explains that Jesus appeared to 500 and disciples and makes a point that many of them are still alive.
Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles. Last of all, as to one untimely born, he appeared also to me. [1 Corinthians 15:6-8 ESV]
The point is clear, these eyewitnesses were there when the event in question happened, and Paul invites his readers to go corroborate what he is saying. Rather than shy away from historical figures and events which can easily be proven or disproven, the Bible if chocked full of such events. Paul is so certain that what he is writing is truth that he invites people to go check it out.
Further support for the reliability of the claims of the Bible, particularly the claims made by the apostles in the New Testament, rests in the persecution they faced from the Roman government and Jewish authorities. Despite rebuke, beatings, prison, attempts on their lives, and eventual martyrdom, not one of the apostles ever recounted on their story. It is hard to believe that every man in that group would have been willing to be persecuted and eventually die for a lie. Furthermore, the Jewish authorities and Roman officials were concerned with the growth of this “sect.” If they had any evidence to disprove the claims of the apostles and disciples, they certainly would have produced it. No such evidence exists!
Finally, there are a number of verses in the Bible where the apostles reiterate that they story they are recording is not something they learned second hand but something which they were eyewitnesses to.
For we did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. [2 Peter 1:16 ESV]
In the introduction to his famous epistle, John explains that they were witnesses to the Jesus Christ which they proclaimed. They had seen him and heard him firsthand:
That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life– the life was made manifest, and we have seen it, and testify to it and proclaim to you the eternal life, which was with the Father and was made manifest to us– that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us; and indeed our fellowship is with the Father and with his Son Jesus Christ. [1 John 1:1-3 ESV]
In compiling his gospel, Luke relied on numerous eyewitness accounts:
Inasmuch as many have undertaken to compile a narrative of the things that have been accomplished among us, just as those who from the beginning were eyewitnesses and ministers of the word have delivered them to us, it seemed good to me also, having followed all things closely for some time past, to write an orderly account for you, most excellent Theophilus, [Luke 1:1-3 ESV]
In the sequel to the Gospel of Luke, Luke explains in Acts that Jesus appeared to his disciples and taught them for the forty days prior to his ascension:
In the first book, O Theophilus, I have dealt with all that Jesus began to do and teach, until the day when he was taken up, after he had given commands through the Holy Spirit to the apostles whom he had chosen. He presented himself alive to them after his suffering by many proofs, appearing to them during forty days and speaking about the kingdom of God. [Acts 1:1-3 ESV]
In the Gospel of John, John explains that Jesus performed miracles and signs in the presence of the disciples so that people would believe he was the Christ. Jesus’ plan included the use of eyewitness testimony to his divinity:
Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name. [John 20:30-31 ESV]
This sentiment is echoed in the book of Acts:
“Men of Israel, hear these words: Jesus of Nazareth, a man attested to you by God with mighty works and wonders and signs that God did through him in your midst, as you yourselves know–[Acts 2:22 ESV]
Peter, in exhorting his fellow elders, reminds them that he was an eyewitness:
So I exhort the elders among you, as a fellow elder and a witness of the sufferings of Christ, as well as a partaker in the glory that is going to be revealed: [1 Peter 5:1 ESV]
Finally, in his defense before Festus and King Agrippa, Paul reminds the rulers that Jesus’ miracles and ministry were not done in secret. Rather, they were done in plain view as a testimony to who Jesus was and to allow those eyewitnesses to accurately record what they had seen:
And as he was saying these things in his defense, Festus said with a loud voice, “Paul, you are out of your mind; your great learning is driving you out of your mind.” But Paul said, “I am not out of my mind, most excellent Festus, but I am speaking true and rational words. For the king knows about these things, and to him I speak boldly. For I am persuaded that none of these things has escaped his notice, for this has not been done in a corner. King Agrippa, do you believe the prophets? I know that you believe.” And Agrippa said to Paul, “In a short time would you persuade me to be a Christian?” [Acts 26:24-28 ESV]
In conclusion, the eyewitness evidence is overwhelming. Jesus intentionally created eyewitnesses to attest to what he had done. Those eyewitnesses accurately recorded what they had seen. Those writings were done when other eyewitnesses were still around and could have refuted the Biblical account. Despite this, there is no record of this happening. Finally, the Jewish and Roman authorities could easily have squashed this “sect” by producing evidence that the accounts of Jesus were untrue. They were never able to produce such evidence.