“Because you have so little faith. I tell you the truth ...” (Matthew 17:20-21)

“Because you have so little faith. I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there’ and it will move. Nothing will be impossible for you.” (Matthew 17:20-21)
This statement follows this question and circumstance:
"Lord, have mercy on my son," he said. "He has seizures and is suffering greatly. He often falls into the fire or into the water. I brought him to your disciples, but they could not heal him."
"You unbelieving and perverse generation," Jesus replied, "how long shall I stay with you? How long shall I put up with you? Bring the boy here to me."Jesus rebuked the demon, and it came out of the boy, and he was healed at that moment. Then the disciples came to Jesus in private and asked, "Why couldn't we drive it out?" (Matthew 17:15-19)
Thus Jesus is now responding to his disciples' question, as they could not remove the demon.

“Because you have so little faith."

What does Jesus mean by "faith"? Faith is not simply accepting or proclaiming to others that Jesus existed. Anyone can have faith that a historical person existed. Anyone can claim that Jesus performed miracles.

Faith is also not simply believing that God exists. However, this is not so hard either, because it makes scientific logic that God exists. Even scientifically it makes sense that God exists. Even if the "big bang" theory is accepted, there still must be a source for the atoms that caused the "bang" - not to speak of the love, personality and life that exists within the world.

Rather, Jesus is speaking of trust. Trust in the Supreme Being. Trust that He will take care of us and that He ultimately knows what is best for us.

Faith is also trusting that Jesus, Moses, Abraham, David, Solomon and all the other prophets were telling us the truth about the Supreme Being. Faith means that we trust that they were passing along to us the messages that the Supreme Being gave them to tell us. We are trusting that they knew the Supreme Being and loved God - and that God loved them. We are trusting, above all, that God loves us and cares for us.

This is confirmed by the Greek word πίστις (pistis) being translated to "faith" in the second sentence - the word πίστις means "the character of one who can be relied on."

What did Jesus mean by his mustard seed analogy?

The meaning of the mustard seed analogy by Jesus has often been mistranslated and misinterpreted by ecclesiastical sectarian institutions and their teachers, who emphasize asking God for materialistic things.

Those who focus on receiving "stuff" from the Supreme Being - including wealth, health, family and even winning football games and so on - are attempting to put the Supreme Being into the position of being our servant.

Rather, Jesus' mission was to teach us that we are all God's servants. Our purpose is to love and serve the Supreme Being, not to be waited on by God.

What many people are doing in the name of faith is really testing God. We are saying, "well if God doesn't give me this or give me that then He doesn't exist." This has nothing to do with faith. Rather, this is a lack of faith. A person who trusts the Supreme Being will not need to test Him.

Yet this testing process is exactly what many of the evangelists are doing in the name of Jesus. They are standing on their pulpits making their millions of dollars, and are supposedly helping all these people get what they want in front of the TV cameras so that everyone can have faith that Jesus exists. Some of them will even fake the process by paying people to act as if they were healed.

Furthermore, they promise people that if they send in their donations, the preacher will pray for them and all their desires will be satisfied. Now this is not faith. This is simply abusing innocent people in the name of Jesus.

This is the reason Jesus said:
“Many will come to me on that day, ‘Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles? Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!'” (Matthew 7:22)
Not only does Jesus not accept these people, he called them "evildoers"! Why? Consider this statement, made right before the above statement:
“Not everyone who says to me ‘Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven.” (Matthew 7:21)
So it is one who does God's will that Jesus will accept. Not that we are constantly asking the Supreme Being to do our will.

And what does it mean to do God's will? Doing God's will means trusting in the Supreme Being and following the instructions given to us by His representatives.

Consider what happens if our mother tells us to do something, and we don't know why. What do we do? Do we demand to know why before we will do it? No. We simply will do it, trusting that what our mother is asking us to do is good for us and others. In other words, we are having faith in our mother by doing what she asks.

It is no different when we do the Supreme Being's will. It requires us to trust God.

"Nothing will be impossible for you.”

Again, Jesus is not speaking of a person suddenly becoming Superman just because he asks God for something. We might ask God to fix our leg or heal our mother from cancer but that will not necessarily happen. Why not?

Remember that Jesus is speaking to his disciples who were trying to execute service. They were trying to serve Jesus and the Supreme Being. They weren't asking why they were not the king or the world or why they didn't have a million dollars.

And the Greek word being translated to "impossible" - ἀδυνατέω (adynateō), which means "not to have strength, power, or ability, to be weak" according to the lexicon.

As such, Jesus is speaking of the Supreme Being giving those who want to serve Him the strength to do their service.

This is why this statement is being attached to the word πίστις (pistis) - which is speaking of reliance upon the Supreme Being. Relying upon God means accepting that if He wants me to do something, I will be given the strength to do it.

It is not as if we somehow want to grab onto faith, and then start trying to dominate the world by moving mountains around. In fact, having faith - trusting God - would automatically delete our thinking that we would need to move any mountains. We would simply have faith that if the Supreme Being thought the mountains needed to move, then they would be moved.

On the other hand, if we were trying to serve God, and the mountains needed to move in order to complete our service to the Supreme Being, we would have confidence that the Supreme Being would see that the mountains were moved. Otherwise, there would be no need to move any mountains.

And this was precisely what was taking place with Jesus' disciples and Jesus. The Supreme Being wanted to show the people that He had empowered Jesus - because Jesus was teaching others about the Supreme Being. This is why He gave Jesus the ability to remove demons. His disciples were not being given that ability at this time - although later we find that after Jesus left the planet some of his students became empowered in that way.

This is because they were trusting in the Supreme Being. Having faith in God means trusting Him.