Jesus said unto him, If thou canst believe, all things are possible to him that believeth. And straightway the father of the child cried out, and said with tears, Lord, I believe; help Thou mine unbelief. – Mark 9:23, 24

It is a great mistake to fancy that to endorse sound doctrine is the same thing as possessing saving faith, for while saving faith accepts the truth of God, it mainly concerns itself with the person and work of the Lord Jesus Christ, and its essence lies in reliance upon Jesus Himself. I am not saved because I believe the Scriptures, or because I believe the doctrines of grace, but I am saved if I believe Christ; or, in other words, trust in Him. Jesus is my creed. He is the truth. In the highest sense the Lord Jesus is the Word of God. To know Him is life eternal. By His knowledge He justifies many. I do not know that the father in the narrative before us had heard many sermons. I am not sure that he had very clear notions about everything that concerned the Savior’s kingdom: it was not essential that he should have in order to obtain a cure for his son. It was a very desirable thing that he should be an instructed disciple, but in the emergency before us the main thing was that he should believe Christ to be both able and willing to cast the devil out of his son. Up to that point he did believe; and, though his faith may have been deficient as well in breadth as in depth, yet it enabled him to realize that the Messiah who stood before him was the Lord, and it led him to place all his reliance upon Him. He did not believe in the disciples; he had once trusted them and failed. He did not believe in himself; he knew his own impotence to drive out the evil spirit from his child. He believed no longer in any medicines or men, for doubtless he had spent much on physicians; but he believed the Man of the shining countenance who had just come down from the mountain. When he heard Him say, “If thou canst believe, all things are possible to him that believeth,” he at once said, “Lord, I believe.” ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1033.cfm