Matthew 16:24-28

Then Jesus told his disciples, “If anyone would come after me, let him deny himself and take up his cross and follow me. For whoever would save his life will lose it, but whoever loses his life for my sake will find it. For what will it profit a man if he gains the whole world and forfeits his soul? Or what shall a man give in return for his soul? For the Son of Man is going to come with his angels in the glory of his Father, and then he will repay each person according to what he has done. Truly, I say to you, there are some standing here who will not taste death until they see the Son of Man coming in his kingdom.”

"In verses 24-26, the Lord is telling His disciples that they have a choice. They can listen to Him and place their faith in Him and do what He tells them is necessary. If they do so, they may suffer in this life but they will be rewarded with eternal life. Or they can listen to the Pharisees and others in the world who insist that each man can determine for himself what is necessary for salvation. If they do so, they may gain in this life, but they will lose in eternity. This is a truth that transcends dispensations. Throughout the history of man, salvation has come by placing faith in whatever God said to people at that point in time. But at the same time — for us, it is faith alone in what Christ accomplished on the cross. It is just as wrong to place our faith in what what necessary in other dispensations as it is to reject God’s Word entirely."

repay each person according to what he has done - Psalm 62:12; Proverbs 24:12

Verse 28 is not saying that the kingdom will come while members of the Lord’s audience were still alive. It is saying that some of them would see the Transfiguration (Matthew 17:1-8), when Jesus appeared in His majesty. This was a taste of what it will be like at His second coming when He returns in glory. Peter refers to this event in his second epistle. It could also refer to "the taste" of "the powers of the age to come" they experiences at Pentecost.

For we did not follow cunningly devised fables when we made known to you the power and coming of our Lord Jesus Christ, but were eyewitnesses of His majesty. For He received from God the Father honor and glory when such a voice came to Him from the Excellent Glory: “This is My beloved Son, in whom I am well pleased.” And we heard this voice which came from heaven when we were with Him on the holy mountain. And so we have the prophetic word confirmed, which you do well to heed as a light that shines in a dark place, until the day dawns and the morning star rises in your hearts (2 Pet 1:16-19).

For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, to restore them again to repentance, since they are crucifying once again the Son of God to their own harm and holding him up to contempt (Heb 6:4-6).