Question: In Mark 9:24, a man tells our Lord Jesus that he believes but asks him to help him with ...

Response: Mark:9:24And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief.
See All... is a precious verse for us. It reads, "straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief."

Simply put, even as born-again believers we have doubts. As for the father of this child, he may have intellectually believed that the Lord was absolutely capable of healing, but as a human, he knew very well his own capacity to doubt. In Mark:9:23Jesus said unto him, If thou canst believe, all things are possible to him that believeth.
See All..., Jesus had specifically stated, "If thou canst believe, all things are possible to him that believeth" (our emphasis). It was his own capacity for belief that gave reason for his cry, "Lord, I believe; help thou mine unbelief."

When it comes to our need for healing, as believers we long for the time when the Lord "shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself" (Phil:3:21Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself.
See All...). "And...ourselves also, which have the first fruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, the redemption of our body" (Rom:8:23And not only they, but ourselves also, which have the firstfruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, the redemption of our body.
See All...).

In the meantime, we must cast ourselves entirely upon the Lord for our deliverance, remembering that when we acknowledge, as this father did, that our faith is weak, He is strong, no matter what the issue, affliction, need, or fear may be. The Bible tells us that our Savior is "touched with the feeling of our infirmities" (Heb:4:15For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
See All...). And whether or not He chooses to heal the illness or solve the problem or deliver us from the issue, even still we can take comfort knowing that He will never fail nor forsake us (Dt 31:6; Josh:1:5There shall not any man be able to stand before thee all the days of thy life: as I was with Moses, so I will be with thee: I will not fail thee, nor forsake thee.
See All...), and that He will strengthen and sustain us until the very end (Ps:55:22Cast thy burden upon the LORD, and he shall sustain thee: he shall never suffer the righteous to be moved.
See All...).