In order to understand how this has been misinterpreted, we need to compare the two versions in the gospels which records the same incident. In this incident the distraught father of a boy who suffered from severe epilepsy went to see Jesus after experiencing great disappointment seeing the disciples fail to heal his son.

First, Mark’s chapter 9 version:

17 A man in the crowd answered, “Teacher, I brought you my son, who is possessed by a spirit that has robbed him of speech. 18 Whenever it seizes him, it throws him to the ground. He foams at the mouth, gnashes his teeth and becomes rigid. I asked your disciples to drive out the spirit, but they could not.”

19 “You unbelieving generation,” Jesus replied, “how long shall I stay with you? How long shall I put up with you? Bring the boy to me.”

One interpretation of this verse has Jesus rebuking the father for being the “unbelieving generation”.

20 So they brought him. When the spirit saw Jesus, it immediately threw the boy into a convulsion. He fell to the ground and rolled around, foaming at the mouth. 21 Jesus asked the boy’s father, “How long has he been like this?” “From childhood,” he answered. 22 “It has often thrown him into fire or water to kill him.

But if you can do anything, take pity on us and help us.” 23 “‘If you can’?” said Jesus. “Everything is possible for one who believes.”

Traditionally we are taught that Jesus is rebuking the father for saying “but if you can do anything, take pity on us and help us”. Then according to this interpretation, Jesus tells the father that if he would simply believe, everything would be possible for him.

24 Immediately the boy’s father exclaimed, “I do believe; help me overcome my unbelief!”

The traditional interpretation has the father acknowledging his unbelief, thus putting the blame for the son not being healed primarily on himself. But as we shall see later, this is unwarranted.

25 When Jesus saw that a crowd was running to the scene, he rebuked the impure spirit. “You deaf and mute spirit,” he said, “I command you, come out of him and never enter him again.” 26 The spirit shrieked, convulsed him violently and came out. The boy looked so much like a corpse that many said, “He’s dead.” 27 But Jesus took him by the hand and lifted him to his feet, and he stood up.

28 After Jesus had gone indoors, his disciples asked him privately, “Why couldn’t we drive it out?” 29 He replied, “This kind can come out only by prayer.”

Here Jesus releases his disciples from any responsibility for failing to drive out the demon. “This kind” of very powerful demon, according to the traditional understanding, comes out only when we pray fervently to God asking God Himself to drive it out. We can only pray and trust God to perform the miracle. If anyone was to blame for unbelief, it would be the father.

Based on this interpretation of Mark 9 therefore, it is taught that the burden of “faith” or “believing” for healing is on the shoulders of the sick person or on his or her family. Part of having “faith” is simply praying and trusting God. Those who pray or minister to the sick or demonized person have little if any part at all in determining whether or not the person is healed.
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But Matthew’s recounting of the very same incident in Chapter 17 gives us quite different understanding…

Matthew 17:14 When they came to the crowd, a man approached Jesus and knelt before him. 15 “Lord, have mercy on my son,” he said. “He has seizures and is suffering greatly. He often falls into the fire or into the water. 16 I brought him to your disciples, but they could not heal him.”

The father was disappointed when the disciples could not heal his son. He had great hope and even expected the disciples of Jesus—well-known for the miracles he performed—to be able to heal his beloved son.

17 “You unbelieving and perverse generation,” Jesus replied, “how long shall I stay with you? How long shall I put up with you? Bring the boy here to me.” 18 Jesus rebuked the demon, and it came out of the boy, and he was healed at that moment.

In the above verses, Jesus is clearly speaking to his disciples, and not to the father. The “you” is plural. Jesus is very disappointed with his disciples and rebukes them harshly for failing to heal the epileptic boy. Jesus then steps in and heals the boy himself.

19 Then the disciples came to Jesus in private and asked, “Why couldn’t we drive it out?”

The disciples, stung by the rebuke they received from Jesus in the presence of the father, came to Jesus now in private. They wanted to know why they had failed to drive out the demon. Back in Luke 9:1-2 they had already received power and authority to cast out ALL demons and to cure diseases. So they could not understand why the demon would not leave. The crucial answer he gave as to why they failed is completely left out of Mark’s version of the incident.

20 He replied, “Because you have so little faith. Truly I tell you, if you have faith as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.” 

The boy was not healed NOT because of the father’s unbelief. It was because the disciples had little faith: they lacked mountain-moving faith. If they indeed had such faith, nothing would be impossible for them. If they had mountain-moving faith, everything would be possible for them—exactly in accordance with what Jesus said in verse 23 of Mark 9—“Everything is possible for one who believes.”

21 “But this kind does not go out except by prayer and fasting.”

What did Jesus mean by this? When in Matthew 17:17-18 Jesus harshly rebuked his disciples, we conclude that he clearly expected his disciples to have healed the boy. So how in verse 21 above could Jesus be saying that in any case they would not have been able to drive out the powerful demon, and that only God would do it after they prayed and fasted? The traditional explanation of verse 21 therefore makes no sense at all.

We conclude that following prayer and fasting, faith—that is, mountain-moving faith—in the disciples would be built up to the point where they would be able to drive out the demon.

So how do we reconcile Mark’s version and Matthew’s version of the incident? Mark appears to blame the father’s lack of faith, while Matthew blames the disciples’ lack of faith for the son’s failure to be healed. We know that Scripture does not contradict Scripture. Therefore there must be a way to resolve this apparent conflict. And indeed there is.
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For that purpose we will integrate the two accounts…

Mark 9:17 A man in the crowd answered, “Teacher, I brought you my son, who is possessed by a spirit that has robbed him of speech. 18 Whenever it seizes him, it throws him to the ground. He foams at the mouth, gnashes his teeth and becomes rigid. I asked your disciples to drive out the spirit, but they could not.”

Mark 9:19 “You unbelieving generation,” Jesus replied, “how long shall I stay with you? How long shall I put up with you? Bring the boy to me.”
(Matthew 17:17 “You unbelieving and perverse generation,” Jesus replied, “how long shall I stay with you? How long shall I put up with you? Bring the boy here to me.”) 

Mark 9:20 So they brought him. When the spirit saw Jesus, it immediately threw the boy into a convulsion. He fell to the ground and rolled around, foaming at the mouth. 21 Jesus asked the boy’s father, “How long has he been like this?” “From childhood,” he answered. 22a “It has often thrown him into fire or water to kill him.

Mark 9:22b  But if you can do anything, take pity on us and help us.”

Following the father’s severe disappointment seeing the disciples fail to heal his beloved son, a grain a desperation appears in his heart as he stood before Jesus and his disciples. He says to Jesus, “but if you can do anything, take pity on us and help us.”

Mark 9:23 “‘If you can’?” said Jesus. “Everything is possible for one who believes.”

Now the crucial question here is: to whom is Jesus speaking when he says “Everything is possible for one who believes”? Is he speaking to the father, or to his disciples who are present at this moment? A strong clue beckons from below in verse 20 of Matthew 17 where Jesus is clearly addressing his disciples: “Because you have so little faith. Truly I tell you, if you have faith as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.” Note the similarity between the two verses here. “Nothing will be impossible…” and “Everything is possible…”

Therefore in Mark 9:23 above Jesus is addressing his disciples who had just failed to heal the boy due to their little faith and lacking faith as a mustard seed.

Mark 9:22b  But if you can do anything, take pity on us and help us.” 23 “‘If you can’?” said Jesus. “Everything is possible for one who believes.” 24 Immediately the boy’s father exclaimed, “I do believe; help me overcome my unbelief!”

Here Jesus is addressing his disciples with the father present at the scene. He is teaching the disciples that everything is possible for those who believe or equivalently those who have faith. But the father chimes in, exclaiming that actually he does believe. That is why with great expectation he brought his son to the disciples in the first place. Therefore Jesus actually was not saying that the father had unbelief. Rather he was blaming his disciples for having “little faith” (Matthew 17:20). But unaware that Jesus was actually directing his words to his disciples and not to him, the father added “help me overcome my unbelief” even though it was clear that he did believe.

Matthew 17:18 Jesus rebuked the demon, and it came out of the boy, and he was healed at that moment.
(Mark 9:25 When Jesus saw that a crowd was running to the scene, he rebuked the impure spirit. “You deaf and mute spirit,” he said, “I command you, come out of him and never enter him again.” 26 The spirit shrieked, convulsed him violently and came out. The boy looked so much like a corpse that many said, “He’s dead.” 27 But Jesus took him by the hand and lifted him to his feet, and he stood up.)

Matthew 17:19 Then the disciples came to Jesus in private and asked, “Why couldn’t we drive it out?”
(Mark 9:28  After Jesus had gone indoors, his disciples asked him privately, “Why couldn’t we drive it out?”)

Matthew 17:20 He replied, “Because you have so little faith. Truly I tell you, if you have faith as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.” 

Jesus here is clearly blaming his disciples for failing to heal the boy because of their little faith. They lacked faith as a mustard seed, or equivalently mountain-moving faith. The unbelief was not in the father, but on the part of the disciples. For some reason, however, this critical reply to the disciples question “Why couldn’t we drive it out?” is missing in Mark’s account.

Matthew 17:21 “But this kind does not go out except by prayer and fasting.”
(Mark 9:29  He replied, “This kind can come out only by prayer.”)

We conclude that following prayer and fasting, the faith, that is, mountain-moving faith of the disciples would be built up to the point where they would be able to drive out the demon. In Mark 9:23 Jesus declared that “Everything is possible for one who believes. “Everything” includes casting out demons of epilepsy. Therefore the traditional interpretation of Mark 9:29 above focusing on prayer alone and then trusting God to do the rest is incorrect.

In addition, in Luke 9:1 Jesus gave the disciples power and authority to drive out ALL demons. Taking into account Jesus’ answer in Matthew 17:20 as to why the disciples couldn’t drive out the demon: “Because you have so little faith”, his reply to the disciples’ question “Why couldn’t we drive it out?” in Mark 9:28 was NOT “This kind can come out only by prayer”. Rather his answer focused on the importance of prayer and fasting as preparation for them to cast out the powerful demon of epilepsy.
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Conclusion

The popular expression “help my unbelief” which is usually a cry from those who need God’s touch has been misinterpreted and thus misapplied. Rather, if anything, it is more apt to come from the lips of those who fail to minister miraculous healing and deliverance when proclaiming the kingdom of God.

Luke 9:1 When Jesus had called the Twelve together, he gave them power and authority to drive out ALL demons and to cure diseases, 2 and he sent them out to proclaim the kingdom of God and to heal the sick. 

Luke 10:9 Heal the sick who are there and tell them, ‘The kingdom of God has come near to you.’

We must stop using the misinterpretation of Mark 9 as a convenient excuse for our failure to obey Jesus’ commands above when proclaiming the gospel on the Third World mission field. Sadly, our failure has resulted in the Great Commission not being fulfilled in 2,000 years.

We can understand why the expression “help my unbelief” from Mark 9 is so popular in the Church. Instead of compelling disciples of Jesus Christ to learn to use mountain-moving faith boldly to advance his kingdom as Jesus taught in Matthew 17:20, we instead use it to comfort ourselves with regard to “why God doesn’t answer my prayer” despite our desperate cries to Him. In that way we disciples are released from our failure to “heal the sick who are there and tell them, ‘The kingdom of God has come near to you'” for advancing the kingdom of God during these Last Days—a failure due to our lack of mountain-moving faith.