Jesus spoke to the unbelief He found. A father had brought his son to the disciples, and they could not cure him (Matthew 17:16). Jesus' two questions are not asking for information. They ask how long He must keep bearing with people who will not believe. Barnes adds that this "was not an expression of impatience or complaint."

The commentators differ on whom He meant. Barnes calls the words "a reproof for their being so slow to believe that he was the Messiah," and says He applied this "probably to the Jews, and not to his real disciples." Gill says He spoke "not to the disciples, but to the father of the child" and those with him, upbraiding them for staying unbelieving after He had been among them so long. Yet Jesus later tells the disciples that they failed "Because of your unbelief" (Matthew 17:20), so no one in the scene stands fully outside the rebuke.

No one answers Jesus' questions. He does not wait for a reply but says, "bring him hither to me" (Matthew 17:17). Then "Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour" (Matthew 17:18). Luke adds that "they were all amazed at the mighty power of God" (Luke 9:43). Afterward the disciples came to Jesus privately to ask why they had failed (Matthew 17:19).

"Faithless" translates apistos, unbelieving. "Perverse" translates diestrammene, a form of a verb meaning to twist or distort, which is why the ESV says "twisted generation." The verb behind "suffer" is anechomai, to bear with or put up with.

Gill suggests the words seem to be taken from the song of Moses, where Israel is called "a perverse and crooked generation" (Deuteronomy 32:5). In Mark's account the father's own faith wavers. He says, "if thou canst do any thing," and then cries, "Lord, I believe; help thou mine unbelief" (Mark 9:22-24).

This question lets us hear the heart of Jesus. Unbelief mattered to Him. He had shown His power again and again, and still the people around Him struggled to trust Him. Gill hears in "how long shall I be with you?" a hint that in a short time He would be gone from them. A few verses later He tells the disciples that the Son of man will be betrayed and killed (Matthew 17:22-23).

But grief did not make Him turn away. In the same breath He says, "bring him hither to me" (Matthew 17:17). Matthew Henry observes that the case of afflicted children should be brought to God in prayer, and that this story encourages parents to bring their children to Christ. The failure of the disciples did not limit the power of Jesus. Where they could not help, He could.