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. 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," we ourselves heard this very voice borne from heaven, for we were with Him on the holy mountain. (2 Peter 1:16-18)You see here Peter is claiming to be an eyewitness. He's not giving "cleverly devised myths" or some sort of hearsay. No, he was there. In fact, he was one of only three who saw Jesus glorified at the Transfiguration. This is pretty heady stuff. This is authority. This is an Apostle. So it might come as a shock to read what he writes next.
And we have something more sure, the prophetic word, 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, knowing this first of all, that no prophecy of Scripture comes from someone's own interpretation. (2 Peter 1:19-20)Do you see that? Peter says that he was an eyewitness and, as such, deserves to be believed. And then he says, "We have something more sure ..." More sure? More sure than an eyewitness? Yes!
Various translations give us various nuances on the phrase, "more sure." The Douay-Rheims Bible says "more firm". ESV says "more fully confirmed". The Literal Translation of the Holy Bible (LITV) says "more established". You can see different senses in these, but the idea is the same. This is established, confirmed, solid, reliable, certain ... "more sure".
What is more sure than Peter, the eyewitness, the mouthpiece for God, the Apostle? "The prophetic Word." That's right. Peter claims that the Scriptures themselves provide a proven source better than even an eyewitness. "More sure."
Dabble with Scripture if you wish. Tear it apart and lay it, bleeding and dying, on your bookshelf. Assure us that no one but you has figured it out or that no one at all has it figured out or that it just doesn't mean that much anymore. You may even feel like you have a newer and better revelation, personally from God. But you do all of this in the face of a more sure source than the eyewitnesses that saw it. God's Word is proven and the interpretation of the Spirit is true. There is nothing more sure in this world.