1And He said to them, "Assuredly, I say to you that there are some standing here who will not taste death till they see the kingdom of God present with power."
2Now after six days Jesus took Peter, James, and John, and led them up on a high mountain apart by themselves; and He was transfigured before them. 3His clothes became shining, exceedingly white, like snow, such as no launderer on earth can whiten them. 4And Elijah appeared to them with Moses, and they were talking with Jesus. 5Then Peter answered and said to Jesus, "Rabbi, it is good for us to be here; and let us make three tabernacles: one for You, one for Moses, and one for Elijah"-- 6because he did not know what to say, for they were greatly afraid.
7And a cloud came and overshadowed them; and a voice came out of the cloud, saying, "This is My beloved Son. Hear Him!" 8Suddenly, when they had looked around, they saw no one anymore, but only Jesus with themselves.
9Now as they came down from the mountain, He commanded them that they should tell no one the things they had seen, till the Son of Man had risen from the dead. 10So they kept this word to themselves, questioning what the rising from the dead meant.
11And they asked Him, saying, "Why do the scribes say that Elijah must come first?"
12Then He answered and told them, "Indeed, Elijah is coming first and restores all things. And how is it written concerning the Son of Man, that He must suffer many things and be treated with contempt? 13But I say to you that Elijah has also come, and they did to him whatever they wished, as it is written of him."
I think what Jesus is talking about by them seeing the kingdom of God present with power is referring to the transfiguration mentioned in verses 2-4. Being told that you will one day see the kingdom of God present with power is one thing. Actually being faced with it 6 days later is another! Understanding that the person beside you is the Son of God is one thing. Seeing Him in His glory and hearing a voice from heaven proclaiming it is another! Hearing about the prophesies of Elijah and Moses is one thing. Meeting them while knowing their words are being fulfilled today is another!
How would I react in a situation like this? I would be so overwhelmed I would have no idea what to do! I could understand being afraid. Would I be worthy of standing in their presence? I would want to preserve the moment as it would be difficult enough to convince myself it was real. I would be hoping I would have my camera with me! These guys didn't have a camera, but desired to preserve the moment or possibly extend the moment by making three tabernacles.
The voice from heaven saying "This is my beloved Son. Hear Him!" would make me stop in my tracks, especially if I was the one rebuked by Jesus when in my earlier frustration of Jesus saying he must die, I tried to say it shouldn't need to be so. This would be a very humbling experience. One in which you could tell it was only the beginning of whatever is to come.
Sure, Jesus isn't telling me that I will see the kingdom of God present with power before my death, but hasn't he promised a second coming? There is nothing that says it won't happen in my lifetime. Would I react like Peter and be afraid and try to find some way to preserve the moment? Would I try to find some way to halt the moment so more preparations could be made? This is a reaction of someone who isn't ready. Am I ready?
This is twice now that we have heard the voice of God from heaven claiming "This is my Son", the first time being at his baptism. Then it was just before he started on his mission. It sounds like Jesus is getting ready for the next major phase of his work. God is commanding Jesus' friends and followers to listen to Jesus.
It says the disciples questioned what rising from the dead meant. First I thought it meant they just questioned this in their own minds, but I now wonder if it was an open discussion with Jesus. That might explain how they got to the question of how the scribes said Elijah must come first. Jesus agrees that the prophesy is correct, that Elijah would come to restore all things before the Son of Man would go through His suffering and death. At first I thought this was simply referring to the appearance of Elijah just moments ago. But Jesus states Elijah has already come and they did to him whatever they wished. Footnotes in my Bible state that Elijah came as John the Baptist. So yes, he had already been here preparing the way, but they imprisoned John the Baptist and killed him.