Coming to the disciples, Jesus saw a great multitude around them, and scribes questioning them. Immediately all the multitude, when they saw him, were greatly amazed, and running to him, greeted him. He asked the scribes, “What are you asking them?”
One of the multitude answered, “Teacher, I brought to you my son, who has a mute spirit; and wherever it seizes him, it throws him down, and he foams at the mouth, and grinds his teeth, and wastes away. I asked your disciples to cast it out, and they weren’t able.”
He answered him, “Unbelieving generation, how long shall I be with you? How long shall I bear with you? Bring him to me.”
They brought him to him, and when he saw him, immediately the spirit convulsed him, and he fell on the ground, wallowing and foaming at the mouth.
He asked his father, “How long has it been since this has come to him?”
He said, “From childhood. Often it has cast him both into the fire and into the water to destroy him. But if you can do anything, have compassion on us, and help us.”
Jesus said to him, “If you can believe, all things are possible to him who believes.”
Immediately the father of the child cried out with tears, “I believe. Help my unbelief!”
When Jesus saw that a multitude came running together, he rebuked the unclean spirit, saying to him, “You mute and deaf spirit, I command you, come out of him, and never enter him again!”
After crying out and convulsing him greatly, it came out of him. The boy became like one dead, so much that most of them said, “He is dead.” But Jesus took him by the hand, and raised him up; and he arose.
When he had come into the house, his disciples asked him privately, “Why couldn’t we cast it out?” He said to them, “This kind can come out by nothing, except by prayer and fasting.”
They went out from there, and passed through Galilee. He didn’t want anyone to know it. For he was teaching his disciples, and said to them, “The Son of Man is being handed over to the hands of men, and they will kill him; and when he is killed, on the third day he will rise again.”
But they didn’t understand the saying, and were afraid to ask him.
“I believe; help my unbelief.” This statement resonates with the experience of many believers, who realize that faith is not simply an alternative to unbelief. Paul Tillich expressed the nature of faith in declaring that “faith takes doubt into itself.” It is important not to quantify or relativize these two statements. The man does not say something like, “I partly believe and partly doubt,” or “I sort of believe and sort of don’t.” The man believes and also does not believe. Mark’s dialectic of faith is analogous to his christological dialectic, in which Jesus is truly human and truly divine, not partly or sort of each. His affirmation captures the nature of faith as both human act and divine gift.
(M. Eugene Boring and Fred B. Craddock, The People’s New Testament Commentary, p. 148)