Mark 9:
Some manuscripts insert verse 21:
Mark continued:
Did Jesus say "prayer" or "prayer and fasting"?
That's a manuscript issue. I don't know the answer.
More importantly, what did Jesus mean by "This kind cannot be driven out by anything but prayer”?
The live-action showed that Jesus rebuked the demon with a quick and short command. There was no extra time to pray or fast. Jesus said This kind of demon can only be driven by someone who practices intensive prayer rooted in faith accompanied by fasting. Jesus himself had experienced 40 days of fasting in Luke 4:
Jesus came out energized:
See also Fasting and prayer.
Jesus' disciples failed.17 someone from the crowd answered him, “Teacher, I brought my son to you, for he has a spirit that makes him mute. 18 And whenever it seizes him, it throws him down, and he foams and grinds his teeth and becomes rigid. So I asked your disciples to cast it out, and they were not able.”
Their failure had to do with faith or the lack of it.19 And he answered them, “O faithless generation, how long am I to be with you? How long am I to bear with you? Bring him to me.”
i.e., lack of faith from the child's father. The parallel account in Matthew 17:20 And they brought the boy to him. And when the spirit saw him, immediately it convulsed the boy, and he fell on the ground and rolled about, foaming at the mouth. 21 And Jesus asked his father, “How long has this been happening to him?” And he said, “From childhood. 22 And it has often cast him into fire and into water, to destroy him. But if you can do anything, have compassion on us and help us.” 23 And Jesus said to him, “‘If you can’! All things are possible for one who believes.” 24 Immediately the father of the child cried outd and said, “I believe; help my unbelief!”
The failure had to do with the little faith of the father and the disciples.19 Then the disciples came to Jesus privately and said, “Why could we not cast it out?” 20a He said to them, “Because of your little faith.
Some manuscripts insert verse 21:
Again, there is a manuscript textual problem, as in Mark.But this kind never comes out except by prayer and fasting.
Mark continued:
Jesus rebuked the demon with a quick and short command.25 And when Jesus saw that a crowd came running together, he rebuked the unclean spirit, saying to it, “You mute and deaf spirit, I command you, come out of him and never enter him again.”
Jesus had no problem casting it out.26 And after crying out and convulsing him terribly, it came out, and the boy was like a corpse, so that most of them said, “He is dead.” 27 But Jesus took him by the hand and lifted him up, and he arose.
Some manuscripts added "and fasting".28 And when he had entered the house, his disciples asked him privately, “Why could we not cast it out?” 29 And he said to them, “This kind cannot be driven out by anything but prayer.”
Did Jesus say "prayer" or "prayer and fasting"?
That's a manuscript issue. I don't know the answer.
More importantly, what did Jesus mean by "This kind cannot be driven out by anything but prayer”?
The live-action showed that Jesus rebuked the demon with a quick and short command. There was no extra time to pray or fast. Jesus said This kind of demon can only be driven by someone who practices intensive prayer rooted in faith accompanied by fasting. Jesus himself had experienced 40 days of fasting in Luke 4:
The devil tempted Jesus, but Jesus did not give in:2 for forty days, being tempted by the devil. And he ate nothing during those days. And when they were ended, he was hungry.
What was the result of this fasting and temptations?13 And when the devil had ended every temptation, he departed from him until an opportune time.
Jesus came out energized:
Prayer and fasting are training exercises for the increase in faith to defeat the devil.14 Jesus returned in the power of the Spirit to Galilee, and a report about him went out through all the surrounding country. 15He was teaching in their synagogues, and everyone praised him.
See also Fasting and prayer.