Then the disciples came to Jesus privately and said, “Why were we not able to drive it out?”
Here the disciples are astonished at their inability and ask Jesus the reason. Their question shows that they had thought they had sufficient authority, based on their past successes (Matt. 10:1), but as Jesus will note next, they had forgotten that this power does not come from themselves, but through living faith, through praying to God, and through having living fellowship with Him.