Matthew 16:27 “For the Son of Man is to come with his angels in the glory of his Father, and then he will repay everyone for what has been done. 28 Truly I tell you, there are some standing here who will not taste death before they see the Son of Man coming in his kingdom.”
17 Six days later, Jesus took with him Peter and James and his brother John and led them up a high mountain, by themselves. 2 And he was transfigured before them, and his face shone like the sun, and his clothes became dazzling white. 3 Suddenly there appeared to them Moses and Elijah, talking with him. 4 Then Peter said to Jesus, “Lord, it is good for us to be here; if you wish, I[a] will make three dwellings** here, one for you, one for Moses, and one for Elijah.” 5 While he was still speaking, suddenly a bright cloud overshadowed them, and from the cloud a voice said, “This is my Son, the Beloved;[c] with him I am well pleased; listen to him!” 6 When the disciples heard this, they fell to the ground and were overcome by fear. 7 But Jesus came and touched them, saying, “Get up and do not be afraid.” 8 And when they looked up, they saw no one except Jesus himself alone.
Luke 9:23 Then he said to them all, “If any want to become my followers, let them deny themselves and take up their cross daily and follow me. 24 For those who want to save their life will lose it, and those who lose their life for my sake will save it. 25 What does it profit them if they gain the whole world, but lose or forfeit themselves? 26 Those who are ashamed of me and of my words, of them the Son of Man will be ashamed when he comes in his glory and the glory of the Father and of the holy angels. 27 But truly I tell you, there are some standing here who will not taste death before they see the kingdom of God.”
28 Now about eight days after these sayings Jesus[f] took with him Peter and John and James, and went up on the mountain to pray. 29 And while he was praying, the appearance of his face changed, and his clothes became dazzling white. 30 Suddenly they saw two men, Moses and Elijah, talking to him. 31 They appeared in glory and were speaking of his departure, which he was about to accomplish at Jerusalem.
Mark 9:1 And he said to them, “Truly I tell you, there are some standing here who will not taste death until they see that the kingdom of God has come with[a] power.”
2 Six days later, Jesus took with him Peter and James and John, and led them up a high mountain apart, by themselves. And he was transfigured before them, 3 and his clothes became dazzling white, such as no one** on earth could bleach them. 4 And there appeared to them Elijah with Moses, who were talking with Jesus. 5 Then Peter said to Jesus, “Rabbi, it is good for us to be here; let us make three dwellings,[c] one for you, one for Moses, and one for Elijah.” 6 He did not know what to say, for they were terrified. 7 Then a cloud overshadowed them, and from the cloud there came a voice, “This is my Son, the Beloved;[d] listen to him!” 8 Suddenly when they looked around, they saw no one with them any more, but only Jesus.
Seems pretty clear that Jesus is referring to the Transfiguration, as the Gospel writers put the Transfiguration directly after this reference He made. Also, note, Jesus said there are SOME standing here, not ALL.
At the Second Coming, ALL will see Him coming in glory.
Also, there are other references where Jesus talks about impending doom. Some of this refers to the destruction of Jerusalem in 70 AD, when the Old Covenant was permanently ended and all sacrifices stopped. And these warnings of impending doom also have deeper meanings where He is also referencing the end of the world and the Second Coming. Jesus and His words have multiple layers.
God bless you on your spiritual journey, keep the questions coming!****