In his sermon of 1519 on Genesis 4, Luther remarked: "This passage ['The Lord had respect unto Abel'] subverts the entire liberty of our human will. _Hic locus semel invertit universam libertatem voluntatis nostrae._" (Weimar 9, 337.) In a sermon of September 8, 1520, we read: "By nature we are born accursed;... through Christ we are born again children of life. Thus we are born not by free will, not by works, not by our efforts. As a child in the womb is not born by its own works, but suffers itself to be carried and to be given birth, so we are justified by suffering, not by doing." (474.) "Where, then," Luther exclaimed about the same time in his _Operationes in Psalmos,_ "will free will remain? where the doing what one can? _Ubi ergo manebit liberum arbitrium, ubi facere quod in se?_" (5, 544. 74.) In a sermon of February 2, 1521, he said: "Whatever grace is in us comes from God alone. Here free will is entirely dead. All that we attempt to establish with our powers is lost unless He prevenes and makes us alive through His grace. Grace is His own work, which we receive in our hearts by faith. This grace the soul did not possess before, for it is the new man.... The great proud saints will not do this [ascribe everything to God and His mercy]. They, too, would have a share in it, saying to our Lord: 'This I have done by my free will, this I have deserved.'" (9, 573; 5, 544.) Thus Luther, from the very beginning of the Reformation, stood for the doctrine of justification, conversion, and salvation by grace alone. Most emphatically he denied that man though free to a certain extent in human and temporal affairs, is able to cooperate with the powers of his natural, unregenerate will in matters spiritual and pertaining to God. This was also the position which Luther victoriously defended against Erasmus in his _De Servo Arbitrio_ of 1525. Goaded on by the Romanists to come out publicly against the German heretic, the great Humanist, in his _Diatribe_ of 1524, had shrewdly planned to attack his opponent at the most vulnerable point. As such he regarded Luther's monergistic doctrine, according to which it is God alone who justifies, converts, preserves, and saves men, without any works of their own. In reality, however, as presently appeared from his glorious classic on the _sola-gratia_ doctrine, Erasmus had assaulted the strongest gate of Luther's fortress. For the source of the wonderful power which Luther displayed throughout the Reformation was none other than the divine conviction born of the Word of God that in every respect grace alone is the cause of our justification and salvation. And if ever this blessed doctrine was firmly established, successfully defended, and greatly glorified, it was in Luther's book against Erasmus.