In 2 Peter 1:16-21, Peter was writing to encourage and strengthen his readers, living in present day Turkey. They were struggling with the truth of Peter's message, in part because other people had come into their midst with false teaching. He presented them with three ideas to consider and find encouragement in.
First, Peter states that the message he first communicated to them, when he was with them, was historically true. He was not relating myths or fables about the life and death of Jesus.
He was writing as an eyewitness to the death and resurrection, and proclaimed the same message that all the Apostles proclaimed, known as the Apostolic testimony.
Secondly, although Peter was an eyewitness to the life and death of Jesus and had personal experience with these events, he points to something more truthful than personal experience, and the prophetic Word as stated in the Jewish Bible, which, Christians call the Old Testament.
Finally, Peter expands on the certainty of the prophetic Word, by explaining that, in a mysterious way that we humans cannot fully grasp, God so worked and directed the authors to write exactly what He intended them to write. They were not robots, but God used their personalities and varied styles to convey the truths he wanted all of us to know in order to know Him. Today, we can be confident that what we read in our Bibles is the inspired Word of God.
Bible scholars affirm the very highest degree of accuracy in the copies that have come down to us; more than 5,000 early copies exist.
The Bible is not a collection of humans’ high and moral thoughts about God, humans and life, nor is it a book of myths explaining natural phenomena. Rather, the Bible is God's Word, God-breathed, to all of mankind--revealing His answers to our deepest questions: where did I come from, what is my purpose in life, is there forgiveness for my wrongdoings and where are we going after we die.