The day after Jesus’ mountaintop transfiguration experience, he and his three disciples, James, John, and Peter returned to find the remaining disciples in the midst of a conflict with the Jewish scribes and a man whose son was demon possessed. The man told Jesus he had asked his disciples to cast out the demon, but they couldn’t do it (Luke 9:40). The implication being that it was impossible for his disciples to perform such a miracle. Jesus’ response to the man indicated that the reason the healing didn’t take place was not because his disciples lacked the ability, but because of the man’s unbelief (Luke 9:41). Jesus told the man, “If thou canst believe, all things are possible to him that believeth” (Mark 9:23). In other words, Jesus was telling this man that he had to have faith, reliance upon Jesus for salvation, in order for his son to be healed.
Jesus himself was limited by the unbelief of the people he was ministering to in his hometown of Nazareth. The people rejected Jesus because they knew him as the son of Joseph and Mary. It says in Matthew 13:54-58:
And when he was come into his own country, he taught them in their synagogue, insomuch that they were astonished, and said, Whence hath this man this wisdom, and these mighty works? Is not this the carpenter’s son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas? And his sisters, are they not all with us? Whence then hath this man all these things? And they were offended in him. But Jesus said unto them, A prophet is not without honour, save in his own country, and in his own house. And he did not many mighty works there, because of their unbelief.
It appears that even some of Jesus’ own disciples didn’t believe he was their Messiah. After casting the demon out of the man’s son, it says in Matthew 17:19-20:
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.
Apparently, the amount of faith it takes to receive salvation is miniscule compared to the power that one receives as a result of having it. The Greek word Jesus used when he told his disciples they needed to have “faith” was pistis, which means persuasion (4102). “It is related to God with the conviction that God exists and is the creator and ruler of all things, the provider and bestower of eternal salvation through Christ.” One of the reasons some of Jesus’ disciples may not have believed in him at this time was because their faith was being blocked by Satan. After he had explained to them the necessity of faith, Jesus told his disciples “Let these sayings sink down into your ears: for the Son of man shall be delivered into the hands of men. But they understood not this saying, and it was hid from them, that they perceived it not: and they feared to ask him of that saying” (Luke 9:44-45).