“Say to this mulberry tree, 'Be uprooted and planted in the sea'”
If you have faith the size of a mustard seed, you can say to this mulberry tree, 'Be uprooted and planted in the sea,' and it will obey you. (Luke 17:6 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'). Luke's impossible object is not a mountain but the sycamine, the black mulberry, proverbial for its root system; later rabbis said it stood six hundred years in the ground. Uprooting the deepest-rooted tree in the region and planting it in salt water: a double impossibility, answered by a mustard seed's worth of faith.
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.