Hearing the Word of God produces faith. We can't call on God unless we believe and we can't believe unless we hear. Romans 10:13-14.
That's why hearing and healing go hand in hand. Once we hear, we can believe; and once we believe, we can be healed.
Romans 10:17 says, "So then faith cometh by hearing and hearing by the word of God." Hearing God's Word causes faith the rise up on the inside of us. That's why Mark 9:23 says, "All things are possible to him that believeth."
God made it easy for us. He said simply to hear and be healed. So if we are having trouble believing God for our healing, we don't try to work up faith; we back to the Word of God and hear what He said by reading it out loud. Then keep on hearing until faith rises up on the inside.
Healing will be the result.