19 Then the disciples came to Jesus privately and said, “Why could we not drive it out?”
20 And He said to them, “Because of the littleness of your faith; for truly I say to you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible to you.
21 [“But this kind does not go out except by prayer and fasting.”]
The disciples had to have been bewildered. They had cast out demons before. They had even done it without Jesus being present, when they were sent out by him in Matthew 10. Now suddenly they were impotent. This was definitely a blow to their egos. That’s why they approach Jesus “privately.” Their failure had been public, and they were determined not to continue that public embarrassment. Somehow they must have guessed that the problem was with themselves and not with the strength of the demon.
When they heard Jesus’ response, they must have been glad that they didn’t ask him publicly. He describes the disciples as having “little faith,” once again in contrast with the Roman centurion (Mt 8:10) and the Canaanite woman (Mt 15:28). If their faith had been adequate, “nothing will be impossible.” They would even be able to move mountains.
What happened to the disciples faith? Many believe that the Transfiguration happened in part to give Peter, James, and John a glimpse of glory to encourage them. If those three were discouraged, the other 9 probably were too. When we are discouraged, we tend to rely on God less. My view is that in their discouragement and the absence of Jesus, the disciples had tried to perform the exorcism in their own ability rather than trusting God to do it. It’s telling that in Mark’s gospel, when Jesus says, “All things are possible for one who believes,” it is the father, not the disciples, who responds, “I believe; help my unbelief!”
In Mark 9:29 and Matthew 17:21, Jesus specifically mentions that empowered faith comes through prayer. This seems to indicate that the disciples had tried to cast out the demon without praying. (Also note that none of the gospel accounts mentions the disciples praying.) This sounds absurd to us, but I could probably come up with a long list of things I tried to do for God or in his name that I did without devoting myself to prayer first. I’m sure that you could too.
Depending on your translation, Matthew 17:21 might not be in your Bible because it is not in all the manuscripts we have of Matthew. (The KJV and NKJV include it. The NIV, ESV, and NRSV omit it. The NASB includes it but puts brackets around it to indicate that it is disputed.) Mark 9:29 provides confirmation of the prayer portion of Matthew 17:21, so really the only part in question is that this faith comes by prayer and fasting.
Whether this verse was originally part of Matthew or not, I think it tells us the same thing that Mark 9:29 tell us. Faith that is able to perform great things is a faith strengthened by disciplined communion with God. Prayer and fasting are not things that just happened on accident. They are things that are done diligently and on purpose.
I like what Warren Wiersbe says in The Bible Exposition Commentary:
“‘Faith as a grain of mustard seed’ suggests not only size (God will honor even a little faith), but also life and growth. Faith like a mustard seed is living faith that is nurtured and caused to grow. Faith must be cultivated so that it grows and does even greater exploits for God (1 Thes. 3:10; 2 Thes. 1:3). Had the nine disciples been praying, disciplining themselves, and meditating on the Word, they would have been able to cast out the demon and rescue the boy.”
Prayer and fasting are also both connected with seeking the will of God. No matter how great one’s faith, if the act isn’t in God will, God will not perform it. Had the disciples been involved in these, their will would have been conformed to God’s will. The assurance that God’s will was to heal this man’s son (after all, Jesus does heal him) would have also strengthened their faith in his ability to heal him through them.
Things to Reflect on in Light of this Passage:
1. Do I purposefully and diligently seek to cultivate my faith through prayer, fasting, meditating on God’s word, and fellowship with and encouraging other believers?
2. Do I pray for God’s will, guidance, and empowerment before I attempt to do something for him or in his name?
3. Do I truly believe that with God nothing is impossible?