The passive words here, "be lifted up" and "be thown" are important here, though lost in the NIV, because they mean some other power is acting on the mountain.
Also, the word translated as "mountain" here is a play on words that Jesus uses elsewhere, where "mountain" can also mean "mule," implying stubbornness.
Jesus here is referring to our human tendency to second-guess ourselves and be conflicted in our beliefs, but this idea is lost in translation because the Greek word meaning "divided" or "decided" is translated as "doubt," when it has not relationship to trust or faith.
Christ's Words in Matthew as a Guide to 40 Days of Prayer.