THe Testimony of Simon Peter, the Father, and the Holy Spirit--2 Peter 1:16-21

16 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. 17 For when he received honor and glory from God the Father, and the voice was borne to him by the Majestic Glory, “This is my beloved Son, with whom I am well pleased,” 18 we ourselves heard this very voice borne from heaven, for we were with him on the holy mountain. 19 And we have the prophetic word more fully confirmed, to which you will do well to pay attention as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts, 20 knowing this first of all, that no prophecy of Scripture comes from someone's own interpretation. 21 For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.

Before we begin, it may be necessary to back up and also share the events that Peter is referencing here.  You can find Jesus' transfiguration recorded in Matthew 17, Mark 9, and Luke 9.  I'm going to share the account written by Luke, but feel free to read the accounts in Matthew and Mark as well.

Luke 9:28-36 (ESV)
28 Now about eight days after these sayings he took with him Peter and John and James and went up on the mountain to pray. 29 And as he was praying, the appearance of his face was altered, and his clothing became dazzling white. 30 And behold, two men were talking with him, Moses and Elijah, 31 who appeared in glory and spoke of his departure, which he was about to accomplish at Jerusalem. 32 Now Peter and those who were with him were heavy with sleep, but when they became fully awake they saw his glory and the two men who stood with him. 33 And as the men were parting from him, Peter said to Jesus, “Master, it is good that we are here. Let us make three tents, one for you and one for Moses and one for Elijah”—not knowing what he said. 34 As he was saying these things, a cloud came and overshadowed them, and they were afraid as they entered the cloud. 35 And a voice came out of the cloud, saying, “This is my Son, my Chosen One; listen to him!” 36 And when the voice had spoken, Jesus was found alone. And they kept silent and told no one in those days anything of what they had seen.

It is understandable that the veracity of such testimony would be called into question if there were only three witnesses who are all from the inner circle and they all claimed to hear the voice of God from heaven telling them that Jesus was the Son of God and they saw Jesus glorified and speaking to Moses and Elijah, and they knew Him.  Peter's point here is that he is sure these events were real because he experienced them and he got to see the prophecies about Jesus fulfilled before His very eyes.  We may not get to see it as clearly as he did, but he says that one day it will all be abundantly clear to us as if we are no longer depending on the "light" of someone else's testimony (compared to the light of a small lamp), but we will see it for ourselves and the truth will be abundantly clear to us (compared to the light of the Sun).  Until then, we can be certain that the prophecies are true because they come from God the Holy Spirit.