Mt 17:14-20
14When [Jesus and his disciples] came to the crowd a man approached, knelt down before him, 15and said, “Lord, have pity on my son, for he is a lunatic and suffers severely; often he falls into fire, and often into water. 16I brought him to your disciples, but they could not cure him.” 17Jesus said in reply, “O faithless and perverse generation, how long will I be with you? How long will I endure you? Bring him here to me.”
18Jesus rebuked him and the demon came out of him, and from that hour the boy was cured. 19Then the disciples approached Jesus in private and said, “Why could we not drive it out?” 20He said to them, “Because of your little faith. Amen, I say to you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move. Nothing will be impossible for you.”
Little Faith: In the imagery used by Jesus, faith the size of the smallest garden seed (mustard) is enough to move mountains (v 20). Hence “little faith” is powerless because it is practically nothing. It is merely an intellectual assent to something presented; it lacks deep conviction.
The faith that Jesus desires is a complete, trusting faith, the total confidence in God’s power no matter what happens. Peter illustrates what little faith is: he ventures into danger by sharing Jesus’ power to walk on the water, but he loses his focus, yields to his fears, and sinks (Mt 14:22-23).
In the same manner, the disciples who fail as exorcists have ventured to face the dangerous demoniac-lunatic presuming that they share Jesus’ power to exorcise. But they may have lost their focus, gotten distracted by the epileptic seizures, the incredible feats of their opponent, and yielded to their fears. Or they may have used Jesus’ name as a magical tool or instrument, expecting instant results at its mere mechanical utterance.
Little faith must deepen and grow that it may become the faith that trusts totally and commits oneself wholeheartedly.