Psalm 27:13 says, "I had fainted, unless I had believed to see the goodness of the LORD in the land of the living." David said "I would have fainted unless I had believed."
The world says has it backwards. They say, "I will believe it when I see it." That was Martha's problem. Lazarus, her brother, had been dead and in the grave for four days. But Jesus said to her in John 11:40, "Said I not unto thee, that, if thou wouldest believe, thou shouldest see the glory of God?" Thomas said, "Seeing is believing," but Jesus said, "Believing is seeing."
David said that had he not believed to see, then he would have fainted. There are many Christians today who are fainting because they are waiting to SEE before they will BELIEVE.
Jesus also said in Matt. 21:22, "And all things, whatsoever ye shall ask in prayer, believing, ye shall receive." Could it be that we are not receiving more because we are not believing God for more?