Matthew 17:20 “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.”
The amount of faith is not all important since only a small amount of faith can do great things. It is the object of our faith which is most important. Our faith must be in God, and nothing else. A sinner does not have to have great faith in order to be saved, but his faith must be in Jesus.