14 At the bottom of the mountain, they were met by a crowd of waiting people. As they approached, a man came out of the crowd and fell to his knees begging, 15 "Master, have mercy on my son. He goes out of his mind and suffers terribly, falling into seizures. Frequently he is pitched into the fire, other times into the river. 16 I brought him to your disciples, but they could do nothing for him." 17 Jesus said, "What a generation! No sense of God! No focus to your lives! How many times do I have to go over these things? How much longer do I have to put up with this? Bring the boy here." 18 He ordered the afflicting demon out - and it was out, gone. From that moment on the boy was well. 19 When the disciples had Jesus off to themselves, they asked, "Why couldn't we throw it out?" 20 "Because you're not yet taking God seriously," said Jesus. "The simple truth is that if you had a mere kernel of faith, a poppy seed, say, you would tell this mountain, 'Move!' and it would move. There is nothing you wouldn't be able to tackle."
Matthew Henry's Commentary on Matthew 17:14-20
Commentary on Matthew 17:14-21
(Read Matthew 17:14-21)
The case of afflicted children should be presented to God by faithful and fervent prayer. Christ cured the child. Though the people were perverse, and Christ was provoked, yet care was taken of the child. When all other helps and succours fail, we are welcome to Christ, may trust in him, and in his power and goodness. See here an emblem of Christ's undertaking as our Redeemer. It encourages parents to bring children to Christ, whose souls are under Satan's power; he is able to heal them, and as willing as he is able. Not only bring them to Christ by prayer, but bring them to the word of Christ; to means by which Satan's strong-holds in the soul are beaten down. It is good for us to distrust ourselves and our own strength; but it is displeasing to Christ when we distrust any power derived from him, or granted by him. There was also something in the malady which rendered the cure difficult. The extraordinary power of Satan must not discourage our faith, but quicken us to more earnestness in praying to God for the increase of it. Do we wonder to see Satan's bodily possession of this young man from a child, when we see his spiritual possession of every son of Adam from the fall!