Matthew 17:9-20

And as they were going down the mountain, Jesus commanded them, “Do not tell anyone what you have seen until the Son of Man has been raised from the dead.” The disciples asked Him, “Then why do the scribes say that Elijah must come first?” He answered and said, “Elijah is coming and will restore all things; but I say to you that Elijah has come already, and they did not recognize him, but did to him as they wished. The Son of Man is also going to suffer at their hands.” Then the disciples understood that He had spoken to them about John the Baptist. [Mal 4:5] When they approached the crowd, a man came up to Jesus, kneeling before Him and saying, [Mark 9:14-27; Luke 9:37-42] “Lord, have mercy on my son, for he is a lunatic (moonstruck) and suffers terribly; for he often falls into the fire and often into the water. And I brought him to Your disciples, and they were not able to heal him.” And Jesus answered, “You unbelieving and perverted generation, how long shall I be with you? How long shall I put up with you? Bring him here to Me.” Jesus rebuked the demon, and it came out of him, and the boy was healed at once. Then the disciples came to Jesus privately and asked, “Why could we not drive it out?” He answered, “Because of your little faith [your lack of trust and confidence in the power of God]; for I assure you and most solemnly say to you, if you have [living] faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and [if it is God’s will] it will move; and nothing will be impossible for you. [Mark 11:23; Luke 17:6; 1 John 5:14]