Faith vs Unbelief

God is able
Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son. (Genesis 18:14 KJV)
Behold, I am the LORD, the God of all flesh: is there any thing too hard for me? (Jeremiah 32:27 KJV)
For with God nothing shall be impossible. (Luke 1:37 KJV)
But Jesus beheld them, and said unto them, With men this is impossible; but with God all things are possible. (Matthew 19:26 KJV)
And he said, The things which are impossible with men are possible with God. (Luke 18:27 KJV)

Amount of faith is not an issue
And Jesus said unto them, Because of your unbelief (ἀπιστίαν): 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. (Matthew 17:20 KJV)

Unbelief is the issue
And he did not many mighty works there because of their unbelief. (Matthew 13:58 KJV)
So we see that they could not enter in because of unbelief. (Hebrews 3:19 KJV)