The story
From Matthew 17:20: “Truly I tell you, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”
Etymology from Wiktionary, CC BY-SA 4.0.
faith will move mountains
Today it means: Belief in oneself (read sometimes as belief in God) can help one overcome any hurdle in life's path. Full definition →