Mark continues his account of Jesus already giving special attention to his identity in chapters 1-7 the core of which is the Father’s command, “This is My beloved Son, listen to him”. It’s this experience on the mountain that Peter and the disciples shared with Jesus that he later says:
16 For we did not follow cleverly devised tales when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of His majesty. 17 For when He received honor and glory from God the Father, such an utterance as this was made to Him by the Majestic Glory, “This is My beloved Son with whom I am well-pleased”— 18 and we ourselves heard this utterance made from heaven when we were with Him on the holy mountain.
19 So we have the prophetic word made more sure, to which you do well to pay attention as to a lamp shining in a dark place, until the day dawns and the morning star arises in your hearts. 20 But know this first of all, that no prophecy of Scripture is a matter of one’s own interpretation, 21 for no prophecy was ever made by an act of human will, but men moved by the Holy Spirit spoke from God. (2 Pet.1:16-21)
These are not cleverly devised tales, they’re real, but there’s something more that you believer need to rely on: the written word of God which is even more real than our own radical experience, it’s weightier than any personal experience you may have. So trust it as you do a torch in the dark to guide your way.