Matthew 17:1-8
The two other times this story of Jesus' transfiguration is told in the Gospels (Mark 9:2-8 and Luke 9:28-36), it always follows right after Jesus said something to the effect of "some of those standing here will not taste death until they see the coming kingdom of God." That's important to note because otherwise you're thinking, "Well, that never happened. Here we are two thousand years later, the disciples are dead, and Jesus still hasn't returned in glory."The transfiguration that Peter, James, and John got to witness apparently was the revelation of the Son of Man coming in his kingdom. Normally we think of Jesus' second coming as a time and space event. It will happen in the future. He will come with the angelic host. The final judgment on mankind will take place. But evidently all that is just so much window dressing because the essence of the coming kingdom is centered on Jesus himself and the revelation of his glory.
Jesus pulled back the veil of his humble fleshly garb, and his entire body from his face to his clothes poured forth blazing light. This is what is means for the kingdom of God to come. The king is revealed in his true glory. Apparently what also got torn back was the veil that separated this world from the world to come, because suddenly Moses and Elijah were hanging out with him chatting, a preview of post-resurrection life.
A lot of people think that life in heaven will just be a return to the Garden of Eden, with a lot of trees and eating fruit and petting animals. But this vision tells us that Jesus' glorified existence, and the existence of everyone who shares in it, will not be about continuing to live in a regular fleshly body that doesn't die. It's about receiving a resurrected body that is full of light, power, and immortality (1 Corinthians 15:42-45, 52-54). Your glorified body is suited for a higher existence in the heavenly kingdom, right alongside the angels. When Jesus preaches the promise of eternal life, this is a picture of what it is.
Remember when the apostle Paul had a similar encounter with Jesus on the way to Damascus (Acts 9:3-6)? It changed his life. In a flash he understood that all his law-keeping was a massive dung heap because he saw Jesus in resurrection glory. Immediately he comprehended that Jesus, not the law, was the way to eternal life.
That's probably what should have happened to Peter, James, and John, but these three were a bit slower than Paul. Instead it ended up being an awkward moment of Peter blathering on about making three tabernacles, because, well, we've all been there. That moment when you feel like you're supposed to say something even though you don't know what, and you end up blurting out something stupid. To make things worse, God the Father rebuked Peter's three tabernacles idea, sending them all diving to the ground in fear. It's another instance of the raw honesty of the Gospel writers. I mean, what a disappointment that the moment of The Big Reveal ended up crumbling into a scene of awkwardness and embarrassment. When it was all over, I could just picture the three of them frazzled, bewildered, and probably wishing they had made a better showing in front of Bible celebrities like Moses and Elijah.
But in the end they did get it. John would later say, "We beheld His glory, glory as of the only begotten from the Father, full of grace and truth" (John 1:14). Peter would say, "But to the degree you share the sufferings of Christ, keep on rejoicing, so that also at the revelation of His glory, you may rejoice with exultation" (1 Peter 4:13). They saw Jesus' glory and wanted to pass it along to the rest of the saints. If only you had been there, you would have seen Hope itself. If you had seen what we saw, you would find courage in your sufferings. And yet you can see him. With eyes of faith you can see what we saw. "And though you have not seen Him, you love Him, and though you do not see Him now, but believe in Him, you greatly rejoice with joy inexpressible, and full of glory" (1 Peter 1:8).