What does Mark 9:19 mean?

In both Matthew 17:17 and Luke 9:41, Jesus is recorded as saying "O faithless and twisted generation." "Faithless" is from the Greek root word apistos and means exactly as it sounds. "Twisted" is from the Greek root word distrepho which means to be turned away from the right path. "Generation" can mean either a group of people who were born within a certain timeframe, or a group with the same ideologies.

Jesus is patient with the disciples, but He won't hold back if they refuse to accept what He has taught them. He has rebuked the Twelve for being hard-hearted (Mark 8:17), and equated Peter's words with those of Satan (Mark 8:33). Jesus has already exposed the scribes' lack of faith (Mark 3:22–30). Matthew 17:20 reveals that if the faithless generation includes the scribes, it includes the disciples, as well.

It's chilling for us to realize that if we do not live in faith of God, we can be lumped together with false teachers who reject Jesus. God does invite us into His work, but not because He needs our own skill or power. We need faith in His power and direction, and we need to be in prayer (Mark 9:29). An effective prayer life reminds us how much we need Him, acknowledges His work around us, and keeps us open to His guidance.