God already knows that we are doubters. Our calling is not to pretend we have no doubts, but to trust Jesus even with our doubts. Do you doubt that God can improve your marriage? Have you become content with your anger or rudeness, suspecting that God cannot help? Do you trust Jesus, but puzzle over why Scripture and sermons don’t move you?
Sooner or later every thoughtful Christian will feel the unsettling, soul-gripping claw of doubt. Some of us might struggle with intellectual doubt. How do I really know God exists? How can I be sure that Jesus is the only way to heaven? Some of us might struggle with circumstantial doubt. How can God be good when there is suffering in the world? If God is my Heavenly Father, why did I lose my job?
In Mark 9, God helps His people process doubt by describing three kinds of unbelief. He contrasts the unbelief of the scribes and His own disciples with that of the father of a demon-possessed boy. As usual the scribes disputed with Jesus and His friends (v. 9), asking trapping, condescending, self-righteous questions, making themselves the prosecutor and Jesus the defendant. This is damning unbelief.
The disciples display a more familiar, “forgetful” unbelief. They thought they could out-maneuver a demon with mere words without prayer and fasting (v. 29). The disciples couldn’t cast out the spirit because of their little faith (Cf. Matt. 17:20; Luke 17:6). John Calvin paraphrases Christ’s response to the disciples’ inability: “You seem as if you were engaged in a mock-battle got up for amusement; but you have to deal with a powerful adversary, who will not yield till the battle has been fought out.” This might sound familiar to us.