Matthew 17:16 Meaning

14And when they were come to the multitude, there came to him a certain man, kneeling down to him, and saying,

15Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water.

16And I brought him to thy disciples, and they could not cure him.

17Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me.

18And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.