Matthew 17:20

He answered, “Because of your little faith [your lack of trust and confidence in the power of God]; for I assure you and most solemnly say to you, if you have [living] faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and [if it is God’s will] it will move; and nothing will be impossible for you.

Luke 17:6

And the Lord said, “If you have [confident, abiding] faith in God [even as small] as a mustard seed, you could say to this mulberry tree [which has very strong roots], ‘Be pulled up by the roots and be planted in the sea’; and [if the request was in agreement with the will of God] it would have obeyed you.

Matthew 13:31

He gave them another parable [to consider], saying, “The kingdom of heaven is like a mustard seed, which a man took and sowed in his field;

Matthew 21:21

Jesus replied to them, “I assure you and most solemnly say to you, if you have faith [personal trust and confidence in Me] and do not doubt or allow yourself to be drawn in two directions, you will not only do what was done to the fig tree, but even if you say to this mountain, ‘Be taken up and thrown into the sea,’ it will happen [if God wills it].

Mark 11:23

I assure you and most solemnly say to you, whoever says to this mountain, ‘Be lifted up and thrown into the sea!’ and does not doubt in his heart [in God’s unlimited power], but believes that what he says is going to take place, it will be done for him [in accordance with God’s will].

1 Corinthians 13:2

And if I have the gift of prophecy [and speak a new message from God to the people], and understand all mysteries, and [possess] all knowledge; and if I have all [sufficient] faith so that I can remove mountains, but do not have love [reaching out to others], I am nothing.

Mark 9:23

Jesus said to him, “[You say to Me,] ‘If You can?’ All things are possible for the one who believes and trusts [in Me]!”

Matthew 14:30-31

But when he saw [the effects of] the wind, he was frightened, and he began to sink, and he cried out, “Lord, save me!”

Matthew 17:9

And as they were going down the mountain, Jesus commanded them, “Do not tell anyone what you have seen until the Son of Man has been raised from the dead.”

Matthew 17:17

And Jesus answered, “You unbelieving and perverted generation, how long shall I be with you? How long shall I put up with you? Bring him here to Me.”

Mark 4:31

It is like a mustard seed, which, when it is sown on the ground, even though it is smaller than all the [other] seeds that are [sown] on the soil,

Luke 1:37

For with God nothing [is or ever] shall be impossible.”

Luke 18:27

But He said, “The things that are impossible with people are possible with God.”

John 11:40

Jesus said to her, “Did I not say to you that if you believe [in Me], you will see the glory of God [the expression of His excellence]?”

1 Corinthians 12:9

to another [wonder-working] faith [is given] by the same [Holy] Spirit, and to another the [extraordinary] gifts of healings by the one Spirit;

Hebrews 3:19

So we see that they were not able to enter [into His rest—the promised land] because of unbelief and an unwillingness to trust in God.

Treasury of Scripture Knowledge

Summary

And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.

Bible References

Because

Matthew 17:17
And Jesus answered, “You unbelieving and perverted generation, how long shall I be with you? How long shall I put up with you? Bring him here to Me.”
Matthew 14:30
But when he saw [the effects of] the wind, he was frightened, and he began to sink, and he cried out, “Lord, save me!”
Hebrews 3:19
So we see that they were not able to enter [into His rest—the promised land] because of unbelief and an unwillingness to trust in God.

A grain

Matthew 13:31
He gave them another parable [to consider], saying, “The kingdom of heaven is like a mustard seed, which a man took and sowed in his field;
Mark 4:31
It is like a mustard seed, which, when it is sown on the ground, even though it is smaller than all the [other] seeds that are [sown] on the soil,

Nothing

Mark 9:23
Jesus said to him, “[You say to Me,] ‘If You can?’ All things are possible for the one who believes and trusts [in Me]!”
Luke 1:37
For with God nothing [is or ever] shall be impossible.”
Luke 18:27
But He said, “The things that are impossible with people are possible with God.”