“Even if you say to this mountain, 'Be taken up and thrown into the sea'”
If you have faith and do not doubt, not only will you do what was done to the fig tree, but even if you say to this mountain, 'Be lifted up and thrown into the sea,' it will happen. (Matthew 21:21 BSB)
What it sounds like today
A literal promise of telekinesis that visibly doesn't happen.
The cultural key
Two idioms stacked. The mustard seed is again the proverb for the tiniest possible quantity. And 'uprooter of mountains' (oker harim) was a rabbinic epithet for a teacher who could resolve seemingly impossible interpretive difficulties; 'moving mountains' was already figurative speech for doing the impossible, the way we use it today ('move heaven and earth'). Spoken beside the withered fig tree on the Jerusalem road, where 'this mountain' has a candidate standing in view: the temple mount. Read with the fig tree's enacted judgment, the impossible-deed idiom picks up a sharper local edge.
Recovered meaning
Not a physics claim: 'even the smallest real faith engages God's power with the genuinely impossible.' The contrast isn't small faith versus big faith; it's faith versus none, and a mustard seed's worth suffices.