An examination of Luther’s lectures on Romans in 1515-1516 reveals significant changes in his understanding of justification. In these lectures, he began to emphasize the believer’s passive role as a recipient of God’s righteousness by grace. Additionally, he explicitly rejected the theological categories of the late medieval scholastics. For example, when Luther commented on Romans 1:17, he stated:
Only in the Gospel is the righteousness of God revealed (that is, who is and becomes righteous before God and how this takes place) by faith alone, by which the Word of God is believed…For the righteousness of God is the cause of salvation. And here again, by the righteousness of God we must not understand the righteousness by which He is righteous in Himself but the righteousness by which we are made righteousness by God. This happens through faith in the Gospel.
Here we can observe Luther’s new understanding of the righteousness of God as something by which God saves believers instead of the perfect standard of God’s Law by which he judges human actions. Following this section, he contrasts Augustine’s emphasis on the gracious gift of God with late medieval scholastic’s focus on human achievement. This rejection of Aristotle’s idea that doing just actions makes one just signified Luther’s complete break from the late medieval scholastic’s adoption of Aristotle’s ethics to explain justification. Instead of doing the right thing to develop the virtue of righteousness, Luther argued that humans receive righteousness by faith as God’s gift, and then do righteous acts. This became a central part of Luther’s teaching on justification.
Luther expanded on this teaching when he examined Romans 4:7. Here he introduces the distinction between inward righteousness and outward righteousness. God imputes righteousness from outside of sinners because inwardly they are unrighteous. Therefore, human beings are not capable of achieving their own inward righteousness. Then, Dr. Luther introduced the famous phrase: simul iustus et peccator (at the same time righteous and a sinner.) He explained in the following manner:
For inasmuch as the saints are always aware of their sin and seek righteousness from God in accord with His mercy, for this very reason they are always also regarded as righteous by God. Thus in their own sight and in truth they are unrighteous, but before God they are righteous because He reckons them so because of their confession of sin. They are actually sinners, but they are righteous by the imputation of a merciful God. They are unknowingly righteous and knowingly unrighteous; they are sinners in fact but righteous in hope.
Following this section, Luther identified as a theological error the belief in the curative power of good works regarding the evil of sin. Sinners are like the half-dead man in Christ’s parable of the Good Samaritan. Christ has brought them to the inn and promised them recovery. Sinners know they still suffer the effects of sin but their hope rests in Christ’s promise of forgiveness. While early Christian theologians (i.e., Augustine and Ambrose) wrote about sin and grace, the scholastic theologians, on the other hand, argued for a performance-based ethic of salvation using Aristotle’s ethics. Luther excoriates the scholastic theologians (pig theologians!) for teaching that “man of his own powers can love God above all things and can performs works of the Law according to the substance of the act, even if not according to the intentions of Him who gave the commandment, because he is not in a state of grace.”
Although Martin Luther became famous because of the publication of the Ninety-Five Theses in November 1517, his scholarly activities had led him to refine his understanding of justification. After completing his lectures on Romans, Luther taught Galatians and Hebrews in 1517 and 1518. However, in September 1517 Dr. Luther had already published the “manifesto of the new reform movement.” This document contained a series of theses against medieval scholastic theology, which Luther had rejected in 1515.
In the theses, Dr. Luther demonstrated his new concentration on the Bible and the writings of Augustine of Hippo. This publication represented a definitive, public refutation of the late medieval scholastic theologians’ emphasis on the ability of human free will to seek God and act lovingly toward Him. He rejected the idea that sinners could prepare themselves to receive God’s grace through any actions. In fact, because of sin, Luther stated that fallen humans have no desire for God or His precepts. The Law exposes evil attitudes and forces people toward certain outward action, but only God’s grace justifies and changes the sinful will.
Luther rejected the integration of Aristotle’s philosophy with Christian theological concepts of grace, justification, and good works. Dr. Luther argued specifically against the application of Aristotle’s ethical teaching to theology. Aristotle taught that humans become more just by practicing justice. Scholastic theologians integrated this idea with Christian theology through teaching that God created a disposition (habitus) of love in the believer’s soul by which the Christian could exercise his will and perform good works to make himself righteous. Luther explicitly rejected this notion when he wrote, “We do not become righteous by doing righteous deeds, but, having been made righteous, we do righteous deeds.”
The following spring Luther participated in a disputation on his theological insights at Heidelberg. By this time, he had become famous because of the Indulgence Controversy. However, in the theses for the Heidelberg disputation Luther expanded his scholarly attacks on scholastic theology. He explained his theology of the cross, which contained the main elements of the doctrine of justification. In thesis 25 Luther concluded, “He is not righteous who does much, but he who, without, work, believes much in Christ.” In the explanation of this thesis, he reversed the scholastic focus on repetitive actions to acquire righteousness. Thereby, he affirmed that faith receives righteousness before the Christian is able to perform good works.
 Martin Luther, Lectures on Romans, Luther’s Works (LW) vol. 25, p. 151.
 LW 25:151-152.
 LW 25:258.
 LW 25:259-261 (quote on p. 261).
 Andrew Pettegree, Brand Luther (New York 2015), 51.
 Martin Luther, Disputation Against Scholastic Theology, LW 31:9-16.
 LW 31:12.
 Martin Luther, Heidelberg Disputation, LW 31:55-56; Martin Brecht, Martin Luther: His Road to Reformation, trans. James L. Schaaf (Minneapolis 1985), 231-234. On the relationship of the theology of the cross to the emergence of the doctrine of justification see Alister E. McGrath, Luther’s Theology of the Cross (Oxford 1985).