Luther on Genesis 15:6

[GHansen]

"Accordingly, lest my discussions obscure what the best interpreter says, I shall speak rather briefly here. Read Paul, and read him most attentively. Then you will see that from this passage he constructs the foremost article of our faith—the article that is intolerable to the world and to Satan—namely, that faith alone justifies, but that faith consists in giving assent to the promises of God and concluding that they are true. 16

In conformity with this fundamental principle, the author of the Letter to the Hebrews learnedly includes the deeds of all the saints in faith and maintains that everything was done by them out of faith. “For without faith it is impossible to please Him” (Heb. 11:6); and the very fact that God promises something demands that we believe it, that is, that we conclude by faith that it is true and have no doubt that the outcome will be in agreement with the promise.

Therefore if you should ask whether Abraham was righteous before this time, my answer is: He was righteous because he believed God. But here the Holy Spirit wanted to attest this expressly, since the promise deals with a spiritual Seed. He did so in order that you might conclude on the basis of a correct inference that those who accept this Seed, or those who believe in Christ, are righteous.

Abraham’s faith was extraordinary, since he left his country when commanded to do so and became an exile; but we are not all commanded to do the same thing. Therefore in that connection Moses does not add: “Abraham believed God, and this was reckoned to him as righteousness.” But in the passage before us he makes this addition when he is speaking about the heavenly Seed. He does so in order to comfort the church of all times. He is saying that those who, with Abraham, believe this promise are truly righteous.

Here, in the most appropriate place, the Holy Spirit wanted to set forth expressly and clearly the statement that righteousness is nothing else than believing God when He makes a promise."

Luther, M. (1999). Luther’s works, vol. 3: Lectures on Genesis: Chapters 15-20. (J. J. Pelikan, H. C. Oswald, & H. T. Lehmann, Eds.) (Vol. 3, pp. 19–20). Saint Louis: Concordia Publishing House.