Jesus tells his disciples, "And He said to them, 'Because of the littleness of your faith; for truly I say to you, if you have faith the size of a mustard seed, you will say to this mountain, 'Move from here to there,' and it will move." (Mt 17:20)
I knew and have been told that faith is not about how much you have but who/what it is in.
Now, I finally understand how this verse and others - Mt 13:31, Mk 4:31, Lu 13:19, and Lu 17:6 - actually teach that point.
Jesus is actually chiding his disciples in Mt 17:20 - something He did several times in the Gospel accounts - for the immaturity ("littleness") of their faith and especially as applying it to external things, in this case failing to cast out a demon.
On one hand their immaturity was somewhat understandable because they had not yet seen the post-resurrection, risen Christ. Compare this "littleness" and powerlessness of faith as compared with what these same disciples did in Acts.
Yet, even for not having yet experienced the resurrection, they have still been with Jesus and have seen His power. Perhaps again, their lack of maturity is because their faith was still an external thing that they had not yet experienced internally.
The woman with the issue of blood who was healed by merely touching Jesus' garment (Mt 9:22) was told by Jesus, "Daughter, take courage; your faith has made you well." She had a personal (internal) experience in the exercise of faith, "Everyone else has failed me. He is my only hope." She reached out for Him in her desperation, and the mountain moved.
The thing that finally struck me is that if Jesus wanted to say the quantity of faith was important, He would not have picked the smallest seed, but rather the largest!
Another thing significant about the smallest seed is found in Mt 13:31 where the smallest seed becomes a great tree. You can't see the great tree in the small seed; that is the result of working faith.
I have just finished reading a great book by Timothy Keller, The Reason for God, Belief in an Age of Skepticism. He gives this excellent illustration of the importance of what your faith is placed in:
"The faith that changes the life and connects to God is best conveyed by the word "trust.' Imagine you are on a high cliff and you lose your footing and begin to fall. Just beside you as you fall is a branch sticking out of the very edge of the cliff. It is your only hope and it is more than strong enough to support your weight. How can it save you? If your mind is filled with the intellectual certainty that the branch can support you, but you don't actually reach out and grab it, you are lost. If your mind is instead filled with doubts and uncertainties that the branch can hold you, but you reach out and grab it anyway, you will be saved. Why? It is not the strength of your faith but the object of your faith that actually saves you. Strong faith in a weak branch is fatally inferior to weak faith in a strong branch. (emphasis added)"
