I have never met a human being who does not believe in naturalism. I have heard of the theory that all nature and everything before death is an illusion. That seems incredible, and is probably a reason that the masses choose atheist over theism.
The difference between atheists and theists is not that theists do not believe in nature. We believe in something beyond nature just as we believe in nature. However, our minds are limited by nature, therefore our faith is limited by nature. It is completely impossible for any Christian to look at a mountain and think without a shadow of doubt that they can move it.
Our naturalism interferes with our faith, and this is not something that we can change. Our minds are part of nature, and they will not allow us to have absolute faith that we can move a mountain from here to there.
This is not a cop-out, it is an answer. That passage is to be taken figuratively. If it were a fake story, the writers of such a story would not insert such a bold claim as "You can move a mountain," because this claim would be instantly rebuked when people realize that they are not moving mountains.
The New Testament is an extremely thorough, detailed account of a man who either truly did live or a fictional character that they tried to pass off as true. If the latter, the writers indicated that they are smart enough to not include fallible claims such as "You can move a mountain."
Just know that you can safely take this phrase an analogy or a faith ideal; something that we should aim for. Similarly to aiming for God's standard despite that we know that we will never reach it.
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