And the apostles said, Lord, increase our faith That we may thus forgive, and neither offend nor be offended. And he said, If ye had faith as a grain of mustard-seed You would be able to overcome all temptations, even those, the conquering of which may be compared to the plucking up of trees and planting them in the ocean, that is, compared to things impossible. 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 undoubtedly proverbial, signifying, not the working of miracles, but the doing of things extremely difficult.
Related Commentaries of Luke 17:5
Luke 17:5-6
5 And the apostles said unto the Lord, Increase our faith.
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.