"Faith" and the Bible don't necessarily go together. "Faith" and Jehovah's Witnesses do, however.
Judaism didn't introduce this concept until the Middles Ages, when Maimonides taught Jews to incorporate it as a translation of some of our words to defend against Protestant proselytizing efforts. The actual word "faith" doesn't appear in the Hebrew Bible. Since the Holocaust, Jews have begun to return to pre-Maimonides vocabulary.
Interestingly, the word "faith" isn't actually in the New Testament either. A product of the Jewish world, there wasn't a concept for "mental assent to a religious concept or doctrine." The word in the Christian Scriptures is PISTIS, which means "faithfulness."
"Faith" is completely static and doesn't require much more than assent from a person. But "faithfulness" is not a static word.
The Jehovah's Witnesses have Jesus saying: "If you have faith the size of a mustard grain, you would say to this black mulberry tree, 'Be uprooted and planted in the sea!' and it would obey you." --Luke 17:6, NWT, 2013 revision.
It sounds ridiculous. Just believe and it will happen?
But note that the word there for "faith" is PISTIS. Also, take into account something about the mustard plant and Jewish law during the Second Temple era in which Jesus lived. Mustard plants are destructive. Their roots burrow and seek out the roots of other plants beyond their own boundaries and suck the nutrients and life of other trees and vegetation. One mustard tree plant can wipe out a neighbor's garden, vineyard or orchard if planted in the wrong spot.
So there were laws devised on where and how mustard grain could and could not be planted, and how they were to be constantly tended with their roots constantly supervised less they destroy other crops and trees. They could literally "tell" another tree "where to go plant itself," so to speak.
Taking this into account, including the right way to translate PISTIS, the verse should read:
If you were as faithful as a grain of mustard, you could be the one saying to a mulberry tree, "Get out of my way and jump into the sea!" And it would have no option but to obey you.
Big difference, right?
Now, the reason for this little lesson in Greek language and Jewish background is to help you see that your question is based on a limited scope: the tiny Watchtower view of the Bible and it's definition of faith.
Is the faith you are questioning really the "faith" mentioned in Scripture? The type practiced in religions? If so, why no introduction of it into Judaism until the Middle Ages and then an abandonment of it after the Shoah? How does that work since the Jews penned the majority of the Bible? That would leave you with a paradox instead of a question.
Then there's the actual meaning of the word "faith." It doesn't mean "a static mental assent to a doctrinal concept or belief." No, the New Testament word means "faithfulness," an action word, to be trustworthy in one's work or way of doing things. How does one have "blind faithfulness" in this sense? Remember the mustard seed illustration? Jesus was teaching people not to go forward blindly, but to have a plan, and to go forward with it "faithfully."
So are we talking faith and the Bible or Watchtower doctrine about faith and the Bible? I think the latter.
