John Calvin Commentary Mark 9:24

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

Lord, I believe. He declares that he believes, and yet acknowledges himself to have unbelief. These two statements may appear to contradict each other, but there is no one among us who does not experience both of them within himself. Since our faith is never perfect, it follows that we are partly unbelievers; but God forgives us and shows such forbearance toward us as to reckon us believers on account of a small portion of faith.

Meanwhile, it is our duty to carefully shake off the remnants of unbelief that cling to us, to strive against them, to pray to God to correct them, and, whenever we are engaged in this conflict, to fly to Him for aid. If we properly examine what portion has been bestowed on each person, it will be evident that there are very few who are eminent in faith, few who have a moderate portion, and very many who have only a small measure.