In Matthew 17, a man comes to Jesus asking Him to heal his demon possessed son. The man had originally gone to the Lord’s disciples to do the job; however, they had been unable to cure the boy. Here’s what the Lord says:
“Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me. And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour. Then came the disciples to Jesus apart, and said, Why could not we cast him out? 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.” (Matthew 17:17-20 KJV)
Faith is currency in the kingdom. You don’t need a lot to get things done but you do need some. Jesus firstly calls His disciples “faithless”... this means that they had no faith to do the task at hand. It’s not that they never had faith but more so that the faith they did have was cancelled out by their unbelief.
1 - 1 = 0. That’s quick maths, right? Similarly, 1 grain of faith - 1 grain of unbelief leaves you with no faith. Our faith must be greater than our unbelief in order for us to be effective. In fact, Jesus tells us that nothing shall be impossible to us with even faith the size of a mustard seed!