In order to correctly interpret a passage such as Matthew 17:20, we first look at the overall context of the passage. Jesus, along with Peter, James and John, had just come down from the “mount of transfiguration,” and they encounter a man with a demon-possessed child. The man tells Jesus that he brought his son to Jesus’ disciples, but they couldn’t cast the demon out (recall that Jesus earlier, in Matthew 10:1, gave His disciples the authority to cast out evil spirits). Jesus then chastises them for their lack of faith and then casts the demon out of the boy. When His disciples inquire as to why the demon didn’t obey their command, Jesus replies with the statement in Matthew 17:20. Their faith, He says, is small and weak. If it were the size of even the smallest of the seeds, the mustard bush, they would be able to “move mountains.”
The first thing that needs to be considered is the Bible’s use of literary techniques. The Bible is first and foremost God’s revealed Word; we want to be clear on this point (2 Timothy 3:16). While the Bible is God’s revealed Word, it is revealed to us by way of language. God condescended—He lowered Himself—to speak to us in ways in which we would understand. Consider a father trying to communicate with his young child. The father has to condescend in order to be understood by the limited intellect and understanding of the child. This is analogous (though not identical) to the way in which God speaks to us.
The Bible employs many forms, or genres, of literature. There is historical narrative, poetry, prophecy, apocalyptic writing, and epistolary literature (to name a few). Among these various literary genres, several literary techniques are used—metaphor, simile, imagery, parable, allusion, irony, personification, paradox, and hyperbole. As readers of the Bible, we must recognize when these techniques are being used so we can properly interpret the meaning. For example, in John 10:7, Jesus says, “I am the door of the sheep.” How are we to interpret this verse? If we are too literal, we might start looking for a doorknob hidden somewhere on His body. However, if we understand this to be a metaphor, then we can begin to understand His meaning (Jesus is the way of access to eternal life, much like a door is the way of access into a room).
Another thing to consider in biblical interpretation is the context of the passage. More often than not, when we take a single verse out of its native context, we end up misinterpreting the verse. In the context of Matthew 17, Jesus rebukes the disciples for their weak faith and says that even if they had mustard seed-sized faith, they could command the mountain to move. Contextually, the mountain must refer to the demon that was afflicting the man’s son. Jesus tells His disciples that, if their faith was stronger, they could have commanded the demon to leave the boy, and it would be so. This was clearly the case in Matthew 10 when Jesus sent them out to cure diseases, cast out demons, and spread the gospel. Therefore, it is clear from the context that Jesus does not intend to assert that mustard seed-sized faith can literally move mountains. Rather, the expression Jesus uses was a common colloquialism of that day; to a Jew of Jesus’ day, a mountain is a metaphor signifying a seemingly impossible task.
Faith that can move mountains is not meant to imply a faith that can literally move literal mountains. The point Jesus was making is that even a little bit of faith—faith the size of a tiny mustard seed—can overcome mountainous obstacles in our lives.