It was a great moment when Peter, James, and John saw Jesus transfigured before them. I believe the real miracle of the transfiguration was not that Jesus shined that day, but that He didn't shine all of the other days as well. He was God incarnate, walking among us. Never at any moment did He cease to be God. He veiled His deity, but He never voided it. At the transfiguration, Jesus allowed Peter, James, and John to get a glimpse of who He really was.
Jesus was not alone on the mountain. Moses and Elijah were there too, talking with Him. Why Moses and Elijah? God gave the Ten Commandments to Moses on Mount Sinai, and Elijah was the greatest of the wonder-working prophets.
I find it interesting that even in this unique situation in which these two men were brought back from glory, they were recognizable. We sometimes think that when we die and go to Heaven, we will be given a new body and identity to the extent that we are almost different people. However, after Jesus rose from the dead and appeared to His disciples, He said, "It is I Myself. Handle Me and see . . . " (Luke 24:39). You still will be you in Heaven, although you will be a perfect version of you.
The blueprint for your glorified body is in the body you now possess. But in Heaven, your body will be like His, because the Bible says, "Beloved, now we are children of God; and it has not yet been revealed what we shall be, but we know that when He is revealed, we shall be like Him, for we shall see Him as He is" (1 John 3:2). Heaven is the earthly life of the believer, glorified and perfected.