If ye have faith, &c. This is the third occasion that this was repeated. The first was in Mat_17:20; Mar_11:23; and the second in Luk_17:6. The condition is quite hypothetical. See App-118.
doubt.App-122.
Be thou removed, &c. It was a common proverb to say of a great teacher, who removed difficulties, that he was "a rooter up of mountains". See note on Luk_17:6.