In the context of 2 Peter, this paragraph - chapter 1 verses 16-21 - is dealing with a very particular issue - namely the future return of Christ. In Peter’s mind, the Transfiguration is proof of both the future return of Christ and the certainty and authority of the Scriptures.
So we’ll really be weaving two major threads together this morning, because that specific application to Peter’s audience and to us also carries with it the broader principle that we ought to pay close attention to Christ and His Word, and to those who give testimony to it, not those who would lead us away from it.