John Calvin Commentary Mark 9:22

"And oft-times it hath cast him both into the fire and into the waters, to destroy him: but if thou canst do anything, have compassion on us, and help us." — Mark 9:22 (ASV)

If you can do anything, have compassion on us, and help us. We see how little honor he renders to Christ; for, supposing him to be some prophet whose power was limited, he approaches him with hesitation. On the other hand, the first foundation of faith is, to embrace the boundless power of God; and the first step to prayer is, to raise it above all opposition by the firm belief that our prayers are not in vain. As this man did not suppose Christ to be at all different from other men, his false opinion is corrected; for our faith must be so formed as to be capable and prepared for receiving the desired favor. In his reply, Christ does not administer a direct reproof, but indirectly reminding the man of what he had said wrongly, points out his fault to him and informs him how a remedy may be obtained.