2 Peter 1:16

For we did not follow cleverly devised myths, etc. Here he touches upon both pagans and heretics, the former of whom did not fear to call whatever pleased them gods; the latter, after receiving the mysteries of the true God, no longer paid attention to the divine Scriptures but instead tried to transfer them by badly interpreting them according to their own erroneous understanding.

The constructions of the heretics are myths and human fantasies, which Paul wants us to avoid, as he writes: "Warn a heretic once or twice, and after that have nothing to do with him." Peter is here already starting to do battle against the heretics. To the extent that they do not possess the truth, heretics are obliged to concoct a lie by using flowery words. But we are not like that, he says, because we saw the truth with our eyes when we were with him on the mountain. Therefore we have the prophets who have proclaimed the same truth to us, and even better, as we came to behold ourselves, the Word came to us. What the prophets foretold, Christ fulfilled when he appeared. We were witnesses of this, and we heard the Father's testimony also.

When Peter had said that they should diligently attend to themselves, and that those things which had been announced to them were indeed so, and he had explained this at length, frequently: although he knew and they had heard in various ways, he now adds their confirmation and says: I do not apply a vain diligence to these matters, but since I know the truth of them to be certain and undoubted, I dwell on them. And what is this? We made known to you the power and coming of our Lord, not by human wisdom with adorned speeches, as if deceiving your hearing with tricks, as the Greeks and heretics do: indeed, the Greeks using elaborate speech and deception; the heretics, however, with fabricated words: just as the Valentinians fleeing into profound depths and silence. For it is likely that they were beginning to arise. Therefore, there is nothing of this kind to be found in us, but we have delivered to you the teaching in a simple and humble manner: which Paul also says to the Corinthians (1 Cor. 2:1): and those things which we have from the sight of our own eyes, we who ascended with him to the holy mountain. Peter says, however, that the Lord showed them on the holy mountain the glory of the Only Begotten (Matt. 17:1), and the voice that they heard from the Father brought down from heaven concerning the Lord. Moreover, since we have known through the things themselves and experience what was proclaimed by the prophets, he says, we judge their prophecy to be more sure through these things: for the things themselves have followed the sayings and oracles.