The effect of Luke's omission of the conversation Jesus had with the disciples about Elijah is clear. This healing appears as the work of the Son of God whom the Transfiguration presented.
"It is the Jesus who has been transfigured who now appears to help men at the foot of the mountain; what the disciples cannot do, he can do. He appears like a visitor from another world who has to put up with the unbelief of men."259
Luke also omitted Jesus' teaching on the importance of faith that He gave His disciples at the end of this story (cf. Matt. 17:19-20; Mark 9:28-29). All Luke's emphasis falls on Jesus' authority.
9:37 Luke is the only Gospel writer who mentioned that the descent happened the day following the Transfiguration. This notation has the effect of contrasting the glorious manifestation on the mountain with the mundane world of sin and unbelief below. Some commentators thought that Luke's comment implies that the Transfiguration happened at night, but that is an unnecessary supposition.
9:38-40 Luke did not identify the boy's condition as epilepsy, as Matthew did (Matt. 17:15). He probably wanted his readers to understand clearly that it resulted from demonic influence (v. 42). Demons produced the symptoms of epilepsy in this boy, though not every case of epilepsy is the result of demon affliction, of course. Unfortunately through history some people have equated epilepsy with demon possession because of the similar symptoms. Doctor Luke described this boy's symptoms more fully than the other Gospel writers, and he alone mentioned that the boy was the only (Gr. monogenes, cf. 8:42; John 3:16) son of his father (v. 38). The failure of the disciples (v. 40, cf. 2 Kings 4:31) set the stage for a great demonstration of Jesus' unique power and authority (v. 42).
9:41-42 Jesus' statement to the father and the crowd (v. 41) recalls Deuteronomy 32:20 where God rebuked the unbelieving Israelites in the wilderness. Jesus went on to express disappointment with these people's lack of faith. By omitting the further conversation between Jesus and the father in which Jesus stressed the importance of faith in Him (cf. Mark 9:21-24), Luke focused attention on Jesus' power. Luke also stressed Jesus' compassion by noting that He gave the boy back to his father (v. 42, cf. 7:15).
9:43a In conclusion, Luke centered attention on the reaction of the crowd. Jesus' miracle amazed (Gr. exeplesonto, cf. 4:32) the people who recognized it as a demonstration of God's great power (cf. 5:25; 7:16, 18; Acts 2:11; 19:27; 2 Pet. 1:16).
This sign should have convinced the crowd that Jesus was God.
(NT only) to listen to the NET Bible 
