Peter speaks to his eyewitness experience of Jesus' transfiguration as a testimony to the truth. When we see the truth revealed to us, spend time with it, listen to it, read and study it, we will know the second something false is presented. The voice of God was very clear to Peter, James, and John. We are to listen to the words of Jesus. If Jesus is the Word and the Truth, there is nothing else we need to combat the darkness and lies of this world.