Commentaries:
Peter is probably referring here to the transfiguration recorded in Matthew 17, Mark 9 and Luke 9. Peter, James, and John were eyewitnesses to that event, and it confirmed to them the prophecies made of old. He then urges us to press forward in faith knowing that the guarantee of the prophecies in God's Word is that they originated in God, not in men. The prophets spoke or wrote as God motivated them by His Holy Spirit. God's very words came through them to us. The Scriptures are not the invention of creative and imaginative men. They are not fairy tales, and we can trust them right on up to the return of Christ and our resurrection because the reputation and power of God are their surety.
John W. Ritenbaugh
God's Promises Are Sure!
When Peter recollected in II Peter 1:16, he was recalling the event in Matthew 17. When Jesus was transfigured, glorified before them, He did not take on a different shape and form than He had before. He still had a recognizable face. He still had clothing on, but everything became shining and bright. Undoubtedly, this was done to impress on the minds of these three men that this Jesus was God in the flesh.
John W. Ritenbaugh
Image and Likeness of God (Part Two)
Other Forerunner Commentary entries containing 2 Peter 1:16:
Matthew 17:1-5
1 Corinthians 15:1-8
2 Peter 1:16