God had promised that He would be the God of Abraham and of his seed forever. Because of this promise there always remain among the Jews those who belong to Christ, and a kingdom of the Jews had to remain for the sake of Christ, who wanted to be born, to preach, and to die there, namely, as the One promised to that nation. Thus that tree was cut down, yet the root and the stump remained, and this out of the pure mercy of God and the superabundance of His grace. In Sodom no survivors remained. This is a a rebuke directed against the saints and the self-righteous—a rebuke especially of those whose conversion through an offering will be impossible. But true conversion is a matter of faith, not of works.
Luther’s Works Vol. 16
Lecture’s on Isaiah ch. 1-39