Therefore let us utterly reject the antinomians, who cast the Law out of the church and want to teach repentance by means of the Gospel.48 It is correct, of course, to say that people should be buoyed up and comforted; but a definition should be added—a definition stating who such people are, namely, that they are those who are wasting away from hunger and thirst in the desert after they have been cast out of their home and country, who sigh and cry to the Lord and are now at the point of despair. People of this kind are fit hearers of the Gospel.
But those who feel that they are in the state of grace because of some physical prerogative, who vaunt their own righteousness and sanctity, do not think they are in the desert. No, they think they are in Paradise. They do not know what it means to wander in the desert. They are not humbled. They are not killed. They must be struck with the hammer of the Law and broken to pieces. Yes, they must be reduced to nothing.
This is done through the Law, which says: “Cast out the slave woman with her son; for he shall not be the heir” (Gal. 4:30); that is, by nature we are all outside God’s grace. For so far as our nature is concerned, we are children of perdition; nor is it of any benefit that the Jews are the descendants of Abraham, that at birth we bring with us the judgment of reason and the Law, and that in some measure we can adjust our will to the Law. All this contributes nothing to salvation.
But whatever there is of the Law, whatever there is of the will of the flesh and of man—of this it is said: “Cast it out!” For God cannot bear the presumption of Ishmael; that is, He does not want us to glory in our physical birth, in our strength, in the freedom of our will, in our wisdom and righteousness. All this must be mortified; all this must be despaired of, just as Hagar despairs in this place.
When this has happened and we have been thrust down into hell, this is the time to call us back by means of the sweet voice of the Gospel, which does not say: “Cast out!” No, it says (Matt. 9:2): “Take heart, my son, your sins are forgiven.” For this reason Scripture says (1 Sam. 2:6) that it is God’s work “to bring down to Sheol and to raise up, to kill and to bring to life.”
Luther’s works, vol. 4: Lectures on Genesis: Chapters 21-25 p 49-50