2 Peter 1:16–21: Eyewitnesses and True Prophecy
Peter's readers faced teachers who treated the second coming as a fabricated story. He answers with what he saw on the mountain and heard from the Father, and with Scriptures that the Spirit carried along.
Luke 1:1–4: An Ordered Account You Can Know
Luke opens his Gospel not with a story but with a claim about how the story was researched and handed down. He writes so that a reader can know the certainty of what he has been taught.
Are the Gospels reliable eyewitness sources? A Biblical Guide
Luke opens his Gospel by naming two supports for its reliability: testimony handed down by those who were eyewitnesses from the beginning, and his own careful tracing of the whole account. He writes so a believer can know the certainty of what he was taught.