Verse explainer

What does Matthew 17:20 really mean?

The point isn't the size of your faith — it's whether the faith you have is real and active, not whether you've accumulated enough of it.

KJV

And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.

BSB

"Because you have so little faith," He answered. "For truly I tell you, if you have faith the size of 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 plain meaning

The disciples had just failed to cast out a demon (v. 16), and they asked Jesus privately why (v. 19). His answer identifies the problem as unbelief — not a shortage of quantity, but a failure of genuine, exercised trust. The mustard-seed image cuts both ways: a mustard seed is tiny, yet it is real, alive, and capable of growth. Jesus is not setting a minimum threshold to clear; he is saying that even a small but genuine faith accomplishes what mere performance of faith cannot. John Gill notes that the disciples were not wholly without faith — their faith was simply unexercised and weak in that moment. The mountain-moving language was a recognized Jewish figure for doing something extremely difficult or seemingly impossible; the apostle Paul picks it up in 1 Corinthians 13:2 with the same sense. The promise is not a blank check for any wish, but a description of what real, trusting dependence on God makes possible when the glory of God and the good of others require it.

The common misreading

"Faith as a mustard seed" means if you just have any faith at all — even the tiniest amount — God must do whatever you ask. This is the verse most often quoted to argue that unanswered prayer means you simply didn't believe hard enough — and that with sufficient faith, any request is guaranteed. But the context dismantles that reading on two counts. First, Jesus is diagnosing a specific failure in a specific moment: the disciples attempted a miracle in a way that apparently relied on their own track record rather than present, trusting dependence on God (v. 19 — they asked 'Why could we not cast it out?'). Second, the mustard-seed image is about the realness and aliveness of faith, not its quantity. Gill and Barnes both note that 'removing mountains' was a standard Jewish figure for accomplishing the extremely difficult — not a promise to reshape landscapes on demand. The closing phrase, 'nothing shall be impossible unto you,' is bounded by what serves God's glory and the good of others, as Gill carefully qualifies. Reading it as an open-ended personal guarantee turns a call to genuine trust into a performance metric — exactly the kind of faith-by-effort that fails the test in verse 20.

What the commentators say

John Gill18th c. · PD

Gill observes that the disciples were not entirely without faith — their faith was simply very weak and unexercised at that moment. He takes the mustard-seed comparison to mean the smallest degree of genuine, active faith, not a faith distinguished by intensity or fervor. The mountain-moving promise, he argues, was fulfilled not necessarily in the literal sense but in equally great and seemingly impossible works the apostles would go on to perform for God's glory.

Matthew Henryearly 18th c. · PD

Henry reads the rebuke as aimed at the quality of their faith in that instance — it was cold, wavering, and unexercised — rather than a permanent deficiency. The mustard-seed figure teaches that a small but sincere and operative faith is sufficient, because the power belongs to God, not to the faith itself. The promise 'nothing shall be impossible unto you' is bounded by the purposes of God's kingdom, not by the believer's personal wishes.

Albert BarnesBarnes' Notes · PD

Barnes stresses that the fault Jesus names is want of faith — specifically, a faith too feeble to be put into action. He takes the mustard seed not as a quality comparison but a size comparison: even the smallest genuine faith is sufficient. He also underscores that 'moving mountains' was a proverbial Jewish expression for surmounting great difficulties, which keeps the promise from being read as a literal formula for altering geography.

The word behind it

ὀλιγοπιστία oligopistia

"Littleness of faith" — a compound of oligos (small, few) and pistis (faith, trust). This is the word Matthew uses here, and it shifts the entire reading: Jesus does not say 'no faith' (apistia) but 'so little faith.' The disciples had faith; it was stunted and unexercised. The word appears only here in the New Testament, making it a precise, deliberate diagnosis rather than a general accusation of unbelief.

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