'Have Faith' in the Bible

and Jesus says to them, On account of your unbelief. For truly I say unto you, If you have faith as a grain of mustard seed, you will say to this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible to you.

And Jesus responding said to them, Truly I say unto you, if you may have faith, and doubt not, not only shall you do that of the fig-tree, but you shall say to this mountain, Be thou taken up and cast into the sea, and it will be done.