Because
Matthew 17:17
Jesus replied, "You unbelieving and rebellious generation! How long will I be with you? How long must I put up with you? Bring him here to Me."
Matthew 14:30
But when he saw the strength of the wind, he was afraid. And beginning to sink he cried out, "Lord, save me!"
Matthew 14:31
Immediately Jesus reached out His hand, caught hold of him, and said to him, "You of little faith, why did you doubt?"
Hebrews 3:19
So we see that they were unable to enter because of unbelief.
If
Matthew 21:21
Jesus answered them, "I assure you: If you have faith and do not doubt, you will not only do what was done to the fig tree, but even if you tell this mountain, 'Be lifted up and thrown into the sea,' it will be done.
Mark 11:23
I assure you: If anyone says to this mountain, 'Be lifted up and thrown into the sea,' and does not doubt in his heart, but believes that what he says will happen, it will be done for him.
Luke 17:6
"If you have faith the size of a mustard seed," the Lord said, "you can say to this mulberry tree, 'Be uprooted and planted in the sea,' and it will obey you.
1 Corinthians 12:9
to another, faith by the same Spirit, to another, gifts of healing by the one Spirit,
1 Corinthians 13:2
If I have [the gift of] prophecy, and understand all mysteries and all knowledge, and if I have all faith, so that I can move mountains, but do not have love, I am nothing.
a grain
Matthew 13:31
He presented another parable to them: "The kingdom of heaven is like a mustard seed that a man took and sowed in his field.
Mark 4:31
It's like a mustard seed that, when sown in the soil, is smaller than all the seeds on the ground.
nothing
Mark 9:23
Then Jesus said to him, " 'If You can?' Everything is possible to the one who believes."
Luke 1:37
For nothing will be impossible with God."
Luke 18:27
He replied, "What is impossible with men is possible with God."