Albert Barnes Commentary Mark 9:24

"Straightway the father of the child cried out, and said, I believe; help thou mine unbelief." — Mark 9:24 (ASV)

Said with tears. The man felt the implied rebuke in the Savior's language. And feeling grieved that he should be thought destitute of faith, and feeling deeply for the welfare of his afflicted son, he wept.

Nothing can be more touching or natural than this. An anxious father, distressed by his son's condition, having applied to the disciples in vain, now coming to the Savior, and not having full confidence that he had the proper qualification to be helped, wept. Any man would have wept in his condition, nor would the Savior turn the weeping supplicant away.

I believe. I have faith. I do put confidence in you, though I know that my faith is not as strong as it should be.

Lord. This word, here, signifies merely master or sir, as it does often in the New Testament. We have no evidence that he had any knowledge of the Divine nature of our Savior, and he probably applied the word as he would have to any other teacher or miracle worker.

Help thou mine unbelief. Supply the defects of my faith. Give me strength and grace to put entire confidence in you. Everyone who comes to the Savior for help needs to offer this prayer. In our unbelief and our doubts we need his aid, nor can we ever put sufficient reliance on him without his gracious help.