What did Jesus mean by "little faith" and "faith like a mustard seed" in Matthew 17:20?

Key facts

• In Matthew 17:20 (NA28), Jesus gives the reason for the disciples' failure as διὰ τὴν ὀλιγοπιστίαν ὑμῶν, "because of your little faith". [NA28, Matthew 17:20]
• Some manuscripts (followed by the King James tradition) read apistian, "unbelief", at Matthew 17:20 instead of oligopistian. This is why some English versions say "unbelief". [NA28 apparatus, Matthew 17:20]
• Oligopistia is formed from oligos ("little, small, poor") and pistis ("faith, trust"). The noun occurs only here in the New Testament. [BDAG, 'ὀλιγοπιστία'; The Weight of God, Ch. 7]
• The related adjective oligopistos ("of little faith") is used by Jesus in Matthew 6:30, 8:26, 14:31 and 16:8. [NA28]
• In Matthew 17:17, Jesus addresses the crowd as an "unbelieving" generation, using apistos, "without faith". [NA28, Matthew 17:17]
• The comparison in Matthew 17:20 is ὡς κόκκον σινάπεως, "like a grain of mustard". The NIV renders it "faith as small as a mustard seed" (NIV), but the word "small" is not in the Greek. [NA28, Matthew 17:20; NIV]
• D. A. Carson reads oligopistia as poverty of faith rather than smallness. The Weight of God reports his description of the disciples' faith as "poor and shoddy". [Carson, Matthew, EBC rev. ed., vol. 9, on Matthew 17:20]
• R. T. France reads the failure as overconfidence in the authority Jesus had delegated to the disciples. [France, The Gospel of Matthew, NICNT, on Matthew 17:14–20]
• The Mishnah (Kilayim 3:2) restricts sowing mustard in a garden bed. [Mishnah, Kilayim 3:2]

Key terms

oligopistia ὀλιγοπιστία

"little faith"; from oligos (little, poor) + pistis; Matthew 17:20

oligopistos ὀλιγόπιστος

"of little faith"; the related adjective Jesus uses elsewhere in Matthew

apistos ἄπιστος

without faith, unbelieving; Matthew 17:17

hōs ὡς

as, like; introduces a comparison

kokkos sinapeōs κόκκος σινάπεως

a grain of mustard seed

Explanation

The story

A father brings his son, who suffers seizures and falls into fire and water, to Jesus' disciples. They try to drive out the demon and fail. This should not have happened. In Matthew 10:1 Jesus had given them authority to drive out impure spirits, and they had used it before. Jesus rebukes the crowd as an apistos ("unbelieving") generation, heals the boy, and then the disciples ask him privately why they could not do it.

Two different diagnoses

Matthew uses two different words here. The crowd is apistos: without faith. The disciples have oligopistia: little or poor faith. The Weight of God (Ch. 7) points out that these are separate diagnoses: "The crowd had nothing. The disciples had something, but it was poverty-stricken."

The book also states that oligopistia "does not appear anywhere in ancient Greek literature before Matthew's Gospel", and that Jesus coined the underlying term. What can be checked directly is that the noun occurs only at Matthew 17:20 in the New Testament, and that the adjective oligopistos appears four other times in Matthew's Gospel. The claim that Jesus coined the term is the book's position, and should be treated as an argument rather than established fact.

The apparent contradiction

Immediately after naming their "little faith", Jesus says that faith like a mustard seed, proverbially the smallest of seeds (Matthew 13:31–32), would be enough to move a mountain. If small faith works, why did the disciples' small faith fail? Translations that add "small" ("faith as small as a mustard seed", NIV) make the tension sharper.

Carson and France: quality and misplacement

D. A. Carson, in his commentary on Matthew (Expositor's Bible Commentary, revised edition, vol. 9), reads oligopistia as poverty, not smallness. As The Weight of God reports his argument, the disciples did expect the exorcism to work, but they treated their authority as a technique that would work automatically. They needed not more faith but true faith: trust in the person who gave them the authority. In the book's summary: "The issue is not the amount, it's the quality."

R. T. France (The Gospel of Matthew, NICNT, 2007) reaches a similar conclusion from another angle. He reads the disciples as having become overconfident in the authority they had been given, expecting it to work because it had worked before. The Weight of God combines the two readings. The disciples' trust shifted from Jesus to their own track record and method.

"Like" a mustard seed, not "the size of"

The Greek hōs (ὡς) introduces a comparison: faith like a grain of mustard. The Weight of God reads it as a comparison of character, not size. A mustard seed is one to two millimetres across but grows into a large, vigorous plant (compare the parable in Matthew 13:31–32). The book points to the Mishnah's restriction on sowing mustard in a garden bed (Kilayim 3:2). It reads this restriction as evidence that mustard was known for spreading aggressively. On this reading, Jesus' hearers would have heard "faith with the character of the most explosively disproportionate seed in our world", not "very small faith". The Mishnah text deals with rules about sowing different kinds of seed together. Its connection to mustard's invasiveness is the book's interpretation.

Seed in the cupboard, seed in the soil

The book's central image is a jar of mustard seeds on a kitchen shelf. The seeds are viable but do nothing until someone plants them. The disciples had real faith in Jesus, the book argues, but at the moment of crisis they were relying partly on themselves. In the book's words: "the size of your faith is irrelevant. What matters is where you plant it."

Common misunderstandings

• "Jesus was telling the disciples to have more faith." Carson and France both read the problem as the quality or placement of their faith, not its quantity. The book agrees.
• "Faith like a mustard seed means a very small amount of faith." The Greek hōs means "like". The word "small" in some translations is interpretive. Many readers do take the point as "even tiny genuine faith is enough", and the book adds that the comparison is about the seed's character.
• "'Little faith' and 'unbelief' mean the same thing in this passage." Matthew distinguishes the crowd's apistos ("without faith") from the disciples' oligopistia ("poor faith"). The reading "unbelief" in some versions comes from a manuscript variant.
• "The disciples failed because they lacked authority." They had received authority in Matthew 10:1. The commentators locate the failure in what they were relying on.
• "Great faith means intense certainty." The book defines great faith as being "fully weight-transferred into Christ", relying on him completely rather than producing a feeling.

What the book argues

The Weight of God (Matthew Wong, 2026), Chapter 7, argues that most teaching on faith wrongly focuses on getting more of it. It defines oligopistia as "poor, misplaced pistis" (Key Terms). The disciples' real but divided trust was resting "half on Jesus and half on themselves", on their track record and delegated power. Drawing on Carson and France, the book reads the mustard-seed saying as being about faith's character and its placement, not its size. Its image is a seed that does nothing in a jar but takes over a garden once planted in soil. The book illustrates oligopistia with a child fighting sleep on her father's chest: trusting him, but not yet fully letting go. The book's prescription is to release the last part of your weight that still rests on yourself. Carson's quality-not-quantity reading and France's misplaced-confidence reading are published scholarship. The soil-and-placement framework, the invasive-mustard reading of the Mishnah, and the claim that Jesus coined the word are the book's own.

In the book: Chapter 7: Good Soil.

Sources

1. Carson, D. A. Matthew. In The Expositor's Bible Commentary, revised edition, vol. 9. Grand Rapids: Zondervan, 2010.
2. France, R. T. The Gospel of Matthew. New International Commentary on the New Testament. Grand Rapids: Eerdmans, 2007.
3. Arndt, William F., F. Wilbur Gingrich, Frederick W. Danker, and Walter Bauer. A Greek-English Lexicon of the New Testament and Other Early Christian Literature, 3rd ed. (BDAG). Chicago: University of Chicago Press, 2000. Entries 'ὀλιγοπιστία', 'ὀλιγόπιστος', 'πίστις'.
4. Mishnah. Compiled c. 200 CE. Kilayim 3:2.
5. Novum Testamentum Graece, Nestle-Aland 28th ed. (NA28).
6. Holy Bible, New International Version (NIV). Biblica, 2011.
7. Wong, Matthew. The Weight of God: How to Believe. Australia, 2026. ISBN 978-1-7646297-3-7.