From The Gospel of Matthew, by Curtis Mitch and Edward Sri, commenting on Matthew 17:1-9
Similar to Christ’s baptism, the transfiguration scene bears witness to the Trinity with the voice of the heavenly Father, the radiance of Jesus the Son, and the glory of the Spirit—signified this time not by a dove but by the cloud (3:16–17). The voice from the cloud repeats verbatim the words of the Father to Jesus at his baptism (3:7): This is my beloved Son, with whom I am well pleased.
But now these words are directed to the three disciples, to confirm their faith in Jesus’ messianic identity in the face of his approaching crucifixion, recently revealed to them (16:16–17, 21).
Also different from the baptism scene is the command to the apostles—listen to him. This recalls the promise of a prophet like Moses, to whom the people are to listen (Deut 18:15, 19), and continues the emphasis in the Gospel on Jesus’ authoritative teaching (5:21–22 passim; 7:24–27; 28:20). This divine command to listen to Jesus reinforces his words in the preceding scenes, which were about his death and resurrection and about the disciples taking up their crosses and following him (16:21, 24–28).
Upon hearing the heavenly voice, the disciples were very much afraid, like the fearful Israelites at Sinai when they heard God’s voice (Exod 20:18–21). In fear and awe, the disciples fell prostrate. When they raise their eyes again, Moses and Elijah have disappeared; Jesus alone remains to complete the work of redemption that those two Old Testament figures foreshadowed.