What does 2 Peter 1:16 mean?

A great number of people believe the claims of Christianity are just fables, folk tales, and legends. Despite the evidence—often, without any at all—these same people are counting on the idea that the Bible is mostly invention with very little truth. Even in Peter's day, this was a counter to the preaching of the gospel. Arguments over the reliability of the message had already begun. Not only had some doubted what they'd been told, but others were trying to take advantage of the situation by making up their own stories. This is something Peter will deal with in the next chapter: clever lies being told about Jesus.

Peter writes that his personal case for Christ is simple: He saw Jesus' majesty with his own eyes. He is reporting as an eyewitness. When Peter preached about Jesus' power and impending return, he wasn't following someone else's script; he was speaking from his own experience.

Specifically, Peter will refer to seeing Christ's "majesty." Peter was present for an event we commonly call the "transfiguration" (Matthew 17:1–8). This is not the only miracle which Peter saw, nor the only piece of evidence he will use. But, for this event is the clearest example of how he knows—for sure—that what he is teaching is the truth.