Moses and Elias. It is significant that this experience was said by Jesus to be a vision rather than the actual physical presence of Moses and Elijah (Matthew 17:9). Moses was dead, whereas Elijah was still living, having been translated into heaven without dying (Deuteronomy 34:5-6; 2 Kings 2:11). So far as Biblical revelation is concerned, all the souls of the Old Testament saints (except Enoch and Elijah) were still confined in Sheol at this time, and were not released until Christ freed them at His death and resurrection (Ephesians 4:8-10). At that time, “many bodies of the saints which slept arose” (Matthew 27:52), but that great event was still in the future at this time.

my beloved Son. This was the second of three occasions on which the Father in heaven validated His Son on earth (see also Matthew 3:17; John 12:28). Many years later, Peter referred again to this voice from heaven (2 Peter 1:17-18).

Jesus only. It is significant that this amazing vision was withdrawn as soon as Peter wanted to place Moses and Elijah on the same level as Jesus (Matthew 17:4). When Peter later described the event in his epistle (2 Peter 1:16-18), he did not even mention Moses and Elijah. This example is important to remember when people supposedly see visions of Mary or other saints associated with Jesus in the past. As He did on the Mount, when people want to idolize such visions, God would say again: “This is my beloved Son … hear ye Him” (Matthew 17:5).

come. The disciples evidently thought that the appearance of Elijah on the Mount was his promised return (Malachi 4:5-6). But now he was gone!

Elias truly shall first come. The Lord Jesus, after telling them that Elijah had only been seen by them in a vision, assured them that He really would come and restore all things, as Malachi had prophesied.

Elias is come already. John the Baptist had come “in the spirit and power of Elijah” (Luke 1:17), as the forerunner of Christ at His first coming, and he had been slain. Elijah will actually return as prophesied, as the forerunner of Christ at His second coming, and he also will finally be slain (see notes on Revelation 11:3-12). Thus, John was a type of Elijah.

Why could not we. The disciples had previously been empowered to cast out evil spirits from demon-possessed people (Matthew 10:1, 8), and presumably had done so. It may be, however, that they had begun to have faith in their own power, rather than in God. If one's faith is in the omnipotent Creator, nothing is impossible (Matthew 17:20), for He controls all things. However, such true faith will also recognize that the prayer of faith will acknowledge dependence on the will of God (Luke 22:42; xTerm 5:14-15).

this kind. A more detailed description of this very extreme case of demonic abuse is given in Mark 9:17-26. See also the note on Mark 9:29.

thou shalt find. This was not a miracle of creation (Jesus did not create the coin out of nothing) but a miracle of providence—that is, controlling and directing natural processes to produce a desired result, one that otherwise would have an almost infinitesimally small probability of occurring.