Jesus spoke into the unbelief all around Him. These two questions are not asking for information. They are a lament over how long He must stay with, and bear with, people who will not believe.

The commentators differ on whom He meant. Gill says Jesus answered the father, "who is included in the reproof afterwards given, for his unbelief, and taking part with the Scribes against his disciples." Where some ancient versions read "them," Gill takes it to mean "not his disciples, but the Scribes and Pharisees, with the father of the child." Writing on the parallel in Matthew 17:17, Barnes says "Jesus applied this, probably, to the Jews, and not to his real disciples," and calls it "not so much an expression of impatience or complaint as a reproof for their being so slow to believe that he was the Messiah." Yet it was the disciples' failure that brought the case to Jesus (Mark 9:18), and in Matthew He tells them they failed "Because of your unbelief" (Matthew 17:20). So the disciples' own faith was also at issue.

Jesus follows His questions with a command: "bring him unto me." They brought the boy, and at once the spirit "tare him; and he fell on the ground, and wallowed foaming" (Mark 9:20). Jesus asked the father how long this had been, heard his plea, "if thou canst do any thing," and answered, "If thou canst believe, all things are possible to him that believeth" (Mark 9:21-23). The father cried, "Lord, I believe; help thou mine unbelief" (Mark 9:24). Jesus rebuked the spirit, took the boy by the hand, "and he arose" (Mark 9:25-27).

"Faithless" is apistos, meaning unbelieving. "Generation" (genea) points beyond one person to the people of that time. "Suffer" is anechomai, to bear with or have patience with. That is why the ESV reads, "How long am I to bear with you?" Barnes explains it: "how long shall I bear with you? How long is it necessary to show such patience and forbearance with your unbelief and perversity?"

The Greek texts differ slightly here. The Textus Receptus, followed by the KJV, says Jesus "answereth him" (the father). Other editions read "them," as the ESV does. Gill notes that several ancient translations also read "them."

These questions show how Jesus regards unbelief. He did not pretend it was nothing. Yet in the same breath He said, "bring him unto me." The rebuke and the invitation come together. His patience was being tested, but it did not run out.

The rest of the story shows where that patience leads. The father, hearing Jesus speak of belief, does not claim a perfect faith. He cries, "Lord, I believe; help thou mine unbelief" (Mark 9:24), and Jesus heals his son. The One who lamented faithlessness is the same One who answers weak faith with power.