By Matt and Abby Joseph, founders of Christian Modern. Matt paints the work, Abby is an interior designer. Last updated: September 2026.
The short answer: Jesus is not grading faith by volume. He tells the disciples they failed through having too little, then says the smallest amount imaginable would have been enough, and the only way both sentences are true is if the contrast is between real faith and none. Moving mountains was also a known figure of speech for making impossible difficulties give way.
He Said It to People Who Had Just Failed
The verse gets printed on mugs without the scene it belongs to, and the scene is a humiliation.
A father brings his son to the disciples. Matthew 17:16 is his sentence, not theirs: I brought him to your disciples, and they could not heal him. A crowd is watching. Jesus heals the boy in a line, and afterwards the disciples come to him privately and ask the question anyone would ask. Why could we not do it?
So Matthew 17:20 is an answer to a failure, given in private, to men who had been authorised to do exactly this back in Matthew 10 and had just discovered that the authorisation did not work the way they assumed.
The Contradiction Inside the Sentence
Read it slowly and it should not hold together.
Jesus says the problem was their little faith. Then he says faith the size of a mustard seed, which the rabbis used as the proverbial example of the infinitely small, would move a mountain.
Too little faith. And the tiniest possible amount is enough. Both in the same breath.
The Greek is where it resolves. The word is oligopistia, a compound of small and faith, and it appears to have been coined for the occasion. The Expositor's commentary renders the sense exactly: too little faith for the occasion. Older manuscripts carry that word, while some later ones read apistia, unbelief, which is the reading behind translations that say "because of your unbelief."
Either way the contrast is not between a small quantity and a large one. It is between faith and something that was not faith. The disciples had authority, a track record, and an expectation that it would work again. That is confidence in a possession. What the mustard seed describes is something different in kind, not in size, and the smallest real amount of it outperforms any volume of the other thing.
Faith as Small as a Mustard Seed puts the figure at the foot of a tree that is already grown, which is the correct proportion. The person is small. The thing that came out of the seed is not.
"Moving Mountains" Was an Idiom
This is the detail that stops the verse being either overclaimed or quietly embarrassed about itself.
In first-century Jewish usage, an outstanding teacher was called a rooter up of mountains. It meant a man who could resolve a difficulty everyone else had given up on. To move mountains was to make the impossible give way.
Paul uses the phrase the same way in 1 Corinthians 13, where he imagines having faith that can move mountains and no love, and nobody reads that as a sentence about geology. Jesus repeats the saying himself a few chapters later about a fig tree and the sea.
So the promise is not that stone will relocate on command. It is larger and more useful than that: the obstruction you have decided is permanent is not necessarily permanent.
The Seed Is Not Only Small. It Grows.
Four chapters earlier Jesus uses the same seed for a different point, and the two readings belong together.
In Matthew 13 the mustard seed is the smallest of seeds that becomes the largest plant in the garden, big enough for birds to nest in. It is not a symbol of smallness. It is a symbol of something that does not stay small.
Which means a faith like a mustard seed is not a permission slip to stay where you are. It is a description of something alive, and the only thing in the picture that is static is the mountain.
I Am The Way is a single road and nothing else, drawn in grounded sage. There is a beige version titled The Path of Life, from Psalm 16, which is the same road on a quieter ground.
The Most Honest Sentence About Faith Is in the Other Account
Mark tells the same story, and his version keeps something Matthew leaves out.
The father, pressed on whether he believes, says: I believe. Help my unbelief.
That is one man holding both things at once and refusing to pretend otherwise, and Jesus heals the boy anyway. Put it next to Matthew 17:20 and the picture completes. The disciples had certainty and it was hollow. The father had a contradiction he admitted out loud, and that counted as faith.
If you are reading this because yours feels too small to be worth anything, that is the sentence to take. Not the mountain. The father's.
A Note on Verse 21
You will often see Matthew 17:20 quoted with a verse 21 attached: this kind does not go out except by prayer and fasting.
It is missing from the earliest manuscripts and most modern translations bracket it, footnote it, or skip from 20 to 22. It almost certainly migrated across from Mark's account of the same incident, where Jesus does say something close to it.
That does not make prayer irrelevant here. It means the point Matthew is making stands on its own, and it is about what kind of faith rather than what quantity of effort.
What to Hang While You Are Still Walking
People reach for this verse during the long middle of something, which is also when they stop expecting anything to change.
The Narrow Gate draws the climb in switchbacks rather than a straight line, which is the honest shape of it. Psalm 118, The Lord Is On My Side is the typographic one, and it is the verse people reach for on the days when the climb is the only thing they can see.
There is also Woman at the Well, who believed on the strength of a single conversation at midday and then went and told an entire town. No track record, no authority, no preparation. A mustard seed's worth, and it moved something.
All four are framed fine art paper prints from $50 unframed to $230 framed. They suit the rooms people pass through rather than sit in, which is why most of this sits in entryway wall art and in prayer room wall art. For what size fits the wall, the room by room guide has the numbers, and the healing in this chapter is the one we picked up from the other direction in the piece on the prayer of faith.
Frequently Asked Questions
What does Matthew 17:20 actually mean?
That the kind of faith matters more than the amount. Jesus tells the disciples they failed through too little faith and then says a mustard seed's worth would move a mountain, which only holds together if the contrast is between genuine faith and something that was not faith at all.
What does faith like a mustard seed mean?
The mustard seed was the rabbis' proverbial example of the smallest thing there is. It is also, in Matthew 13, the seed that becomes the largest plant in the garden. So the image carries both: the smallest real faith is enough, and real faith does not stay that size.
Did Jesus mean we can literally move mountains?
Moving mountains was a known figure of speech. Jewish teachers of the period called an outstanding rabbi a rooter up of mountains, meaning someone who could resolve an impossible difficulty. Paul uses the phrase the same way in 1 Corinthians 13. The promise is that what looks immovable is not necessarily permanent.
Why could the disciples not heal the boy?
Jesus says it was their little faith. They had been given authority to heal in Matthew 10 and appear to have treated it as a capability they owned. The Greek word, oligopistia, carries the sense of too little faith for the occasion rather than a shortfall against some required quantity.
What is the difference between Matthew 17:20 and Mark 9:24?
They are the same incident. Matthew records Jesus explaining the disciples' failure. Mark keeps the father's reply instead: I believe, help my unbelief. Read together, the disciples had certainty that proved hollow and the father had an admitted contradiction that counted as faith.
Is Matthew 17:21 in the Bible?
It is missing from the earliest manuscripts, and most modern translations bracket it, footnote it, or go straight from verse 20 to verse 22. It appears to have been copied across from Mark's account of the same event, where Jesus says something similar about prayer.
What Bible verse is good for when your faith feels small?
Matthew 17:20 and Mark 9:24 together. One says the smallest genuine faith is enough, the other gives you the words for admitting you have doubt and faith at the same time. Psalm 118 and Psalm 16:11 are the other two people reach for during a long stretch.
One Last Thing
Nothing in the passage asks you to work up more belief. It asks what the belief is in. The disciples' mistake was not that they had too little of it, but that what they were trusting had quietly become themselves.