This righteousness of ours comes through faith. Concerning it we should have no doubt; nor should we say that it is useless or vain, lest we hear the words: “Woe to those who call good evil” (Is. 5:20). Therefore I should not say: “I have the blessing, and for this reason I am useless.” No, I must say: “I am honest, saintly, righteous, and blessed, because I am such through the righteousness of another, not through my own righteousness. This I can set against the wrath and judgment of God, and I am sure that God cannot deny Himself and cast aside His Son, that Seed of Abraham. Therefore I maintain with confidence and without any doubt that I am righteous and an heir of eternal life.” This promise embraces almost the entire Christian doctrine, the incarnation of Christ and justification, but not the sacraments, which were revealed later on, when Christ came. Furthermore, it contains a refutation of the papistic doctrine, not only concerning traditions and works but also concerning faith combined with works, which they stress against us “solafideists.” This proposition remains unshakable and sure, that faith alone justifies, because all trust of all men is absolutely condemned, and trust is put in the Seed alone.
Therefore we shall conclude in opposition to our opponents: “Your justification, in which you teach that works must be combined with faith, is a lie, because you contradict yourselves, maintain the righteousness of works, and deny trust. When trust is abolished, righteousness itself must be abolished, because certainty and trust are the very life of righteousness.”
Luther’s works, vol. 4: Lectures on Genesis: Chapters 21-25 p 166-167