Ye might say unto this sycamine-tree, &c.— "If you had but a small measure of faith, it would overcome all temptations; even those, the conquering of which may be compared to the plucking up of trees, and planting them in the ocean." Some, taking this example, by which the efficacy of faith is illustrated, in a literal sense, have supposed that the apostles desired Jesus to increase their faith of working miracles; but the expression is proverbial, signifying not the working of miracles, but the doing of things extremely difficult. See another proverb of the same kind, Matthew 17:20.
Related Commentaries of Luke 17:6
Luke 17:6
6 And the Lord said,If ye had faith as a grain of mustard seed, ye might say unto this sycamine tree, Be thou plucked up by the root, and be thou planted in the sea; and it should obey you.