This great faith does not work if we have hesitation. God can accomplish nothing through us if we harbor doubt.
We cannot be a "but" believer. We cannot say that God is supreme, but I'm not sure if He can cure this cancer. We cannot say I believe God can work miracles of healing, but He cannot help me stop yelling at my children.
When we add a "but" to God we are no longer trusting in Him. Instead we are restricting Him. He does not work under restrictions. If God can work miraculously in one area of your life, He can do the same in every area. If you don't believe it will happen, wholeheartedly, then it doesn't happen. It is as simple as that.
Help me overcome my unbelief.