When somebody is not instantly healed it does not mean that it is not God's will or they did not have enough faith. When Jesus came off of the mount of transfiguration he was met by a man with an epileptic son. The bible goes on to declare that this man had brought his son to the disciples and they could not cure him. If we were to base our theology on the ones who were not instantly healed to support much of the churches unbelief in divine healing. Our experience does not change God's will.
Faith is diligent.
It keeps on asking, seeking and knocking until the door is opened. Sometimes your miracle will take diligence. When someone is not instantly healed in one of our meetings I ask them to come back, again and again and again until they are healed. The bible declares that these three remain faith, hope and love, many died not receiving the promise. We contend for our breakthrough and healing till we die.