Jesus has just been talking to the people and his disciples about following him. Six days later, Jesus goes with three of his disciples up a mountain where his appearance temporarily changes to what he will look like one day in the kingdom of God.
The kingdom of God coming represents God showing himself as king. AT: "God show himself with great power as king" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The author uses the reflexive pronoun "themselves" here to emphasize that they were alone and that only Jesus, Peter, James, and John went up the mountain. (See: [[rc://en/ta/man/translate/figs-rpronouns]])
This can be stated in active form. AT: "his appearance had changed" or "he appeared very different" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Bleaching describes the process of making natural white wool even whiter by using chemicals like bleach or ammonia. AT: "whiter than any person on earth could whiten them"