The Kingdom of God

In verse 1, Jesus mentions that some people in his presence will see the full power of the Kingdom of God on earth before they die.

Since the Transfiguration occurs just 6 days later, it seems odd that Jesus would mention people's deaths in this context.  I would imagine, reading verse 1 in isolation, that Jesus was referring to what we now refer to as the Second Coming.

Another possibility is that Jesus could be referring to his Resurrection.  That is a definite example of the power of the Kingdom of God.

If we accept Matthew Henry's interpretation of verses 1-13, then the Transfiguration is just one of many examples to which Jesus is referring.