Thus Holy Scripture presents the accounts of the saints in such a way that it gives praise to the power of faith. Consequently, he who has the Word of God should consider himself blessed and should turn his eyes away from present things to those that lie in the future and are invisible. For the Word of God, especially the promise, does not speak of present things; it speaks of things that lie in the future and have been experienced by no one. Faith attaches itself to a thing that is still an utter nothing and waits until everything comes about. It is a knowledge and wisdom of darkness and nothingness,29 that is, of things which it has not experienced and are unseen and almost impossible. He who wants to be a Christian must meditate well on and fix this in his heart. For all other branches of knowledge are taught on the basis of syllogisms, inductions, and experiments. They do not have their basis or beginnings in what is nothing, and especially not on what is unseen, impossible, absurd, and foolish; but faith, which takes hold of the promise, fixes the heart on what is altogether absurd, impossible, and contained in the Word and God’s promise.
Luther’s works, vol. 5: Lectures on Genesis: Chapters 26-30 p 128