FAITH AND PROMISE
When something is promised, you have not seen it happen yet, have you? If I promise my wife that I'm going to clean out the basement, there's no proof that you can see. There's only my word. That promise is the only evidence it will happen. And I may prove unreliable for one reason or another.
But God is trustworthy and true. His promises are more reliable than any evidence you can see or touch or reason out. His promises are the unseen proof that give faith it's sureness. They are the unseen evidence that drives away doubt. Faith is certain of what we do not see because of God's promises.