Alister McGrath’s 2011 update of his 1985 book is really about the evolution of Luther’s thought in light of Late Medieval theology. If you want to learn about the theology of the cross, jump to chapter 8, the final chapter. Everything else leads up to that point.

McGrath shows how Luther’s theology up to 1515 is typical of Late Medieval theology north of the Alps. He shows that there is nothing revolutionary about Luther’s 95 theses. The Pope’s authority is not challenged. There is no new theology. He simply posted a typical notice for debate.

In fact, another professor, Andreas Bodenstein (Von Karlstadt) posted 151 theses on the same topic, to the Castle Church door six months earlier. The theology faculty at the University of Paris drew up a critique of the theology of indulgences in May 1518. There were no accusations of heresy.

McGrath defines the three strains that influence Luther’s theology: humanism, nominalism and the Augustinian movement. He also makes a strong case that Luther was educated according to the Via Moderna.

The author spends time discussing the four ways of interpreting scripture, common to the Via Moderna, and employed by Luther. Literal meaning was always first, but allegorical interpretation was also important, per Augustine, who felt everything should edify. So when Augustine comes upon Exodus 23:18, “You shall not boil a kid in its mothers milk,” he doesn’t find it edifying, so, interprets it: “Christ should not himself perish in the slaughter of the innocents.”

A third manner of interpretation is tropological (or moral). Finally there is the anagogical, which was for elevation to the eternal felicity of the saints. These four methods of biblical interpretation make up what is known as the quadriga (after the Roman chariot drawn by four horses).

Following Augustine, Luther interpreted the Old Testament Christologically, as can be seen in his Dictata Super-psalterium, the glosses (comments in the margins) and scholia (extended commentary) Luther makes in the wide-margined version of the Psalms he uses for lecturing.

The quadriga is a characteristic of late medieval Biblical exegesis, and Luther employs it magnificently. It dominates Luther’s exposition of the Psalter.

Luther’s early theology of justification is from the Via Moderna, with a heavy influence of Augustinian theology. Luther finds the prevailing theology of the day Pelagian (a denial of original sin such that humans have the capacity to choose good without divine aid). Salvation is by faith, which Luther interprets as humility in his early theology. We become worthy of grace by acknowledging our sin, recognizing our need of God, and humbling ourselves.

The rest of McGrath’s book focuses on determining when Luther made the shift from the theology of justification from the Via Moderna, to the rejection that humans can do any good works, quod in se est. When did Luther have his breakthrough to a theology of pure grace, where even faith is a gift of God such that he concludes, “I believe that I cannot by my own reason or strength believe in Jesus Christ, my Lord, or come to Him…”

This breakthrough hinges on Luther’s understanding of the “righteousness of God.” Early understandings of this were based on Aristotlean thought, and Cicero’s concept of justice, as giving to each person their due. If the righteousness of God means giving each sinful person what was coming to him or her, where was the good news in this?

When was the breakthrough? Luther says, “When I became a doctor I did not yet know that we cannot make satisfaction for our sins.” There is no reason to doubt Luther here. Luther became a doctor of divinity on October 19, 1512, and began expounding upon the Psalms the year after. So the breakthrough is after 1512.

In a 1545 Table Talk entry, Luther reflects on his early career and on the theological problem that had been troubling him for some considerable period of time: this idea of the righteousness of God. Luther reflects that in 1519 he returned to the study of the Psalter, after lecturing on Romans, Galatians and Hebrews. “The righteousness of God is revealed in it [the gospel].” By meditating day and night on these words: “the righteousness of God is revealed in it,” and “the righteous shall live by faith,” Luther says he came to understand the righteousness of God as a free gift of grace. This opened for him the gates of paradise and made the phrase which he had hated so much now beloved words of hope. He then read Augustine, and realized to his surprise that he interpreted the righteousness of God in the same way, as that which God bestows upon us, by which we are justified. And so He went back and began to interpret the Psalter for a second time.

Table Talk sayings are second hand, and so not as reliable as writings from Luther’s own hand. And the aging Luther may be compressing a longer process of discovery. So the breakthrough happened in 1519 or before.

The author sees in Luther’s lectures a shift taking place around 1515.

Luther at some point concludes that the problem is in scholastic theology, which traps theology in Aristotelian categories. Luther: “In Anselm it simply is not possible to explain iusticia (righteousness) in Ciceronian terms.”

He had been taught according to the Via Moderna: that God gives grace to anyone who does Facere Quod in se est, which literally means “do what lies within you.” Then God will bestow grace. “Do your best and God will do the rest.” Quod in se est was an impossible and unverifiable standard. Luther thought sought to answer the question, “Have I been saved?”

Once Luther came to his new understanding of “the righteousness of God,” which he then discovered in Augustine, this prepared the way for the theology of the cross.

In the Heidelberg Disputation of 1518, Luther presided over the opening of the disputation of the chapter of the Augustinian order at Heidelberg. This disputation concerned series of theses that Luther had drawn up at the invitation of his superior Johannes Von Staupitz.

Thesis 19 said, “Anyone who observes the invisible things of God understood as those things that are created, does not deserve to be called a theologian.”

Thesis 20 said, “But anyone who understands the visible, rearward things of God as observed in the suffering of the cross does deserve to be called a theologian.”

McGrath think the translation of thesis 20 in the English version (manifest things of God) is a flagrant mistranslation.

Just as Moses is denied a full frontal view of the glory of God, only getting a fleeting glimpse of God from behind, so we only get a glimpse of the Deus Absconditus (hidden God). This is revelation: a fleeting glimpse of God.  We can only see God from the rear, the Posteriora Dei.

Luther goes on to distinguish a theologian of glory with a theologian of the cross (who observes what is seen). For Luther, the cross is the normative verbal and iconic centering of Christian thought. Christian theology is based on the crucified God, rather than rational, Aristotelian thought as a secular starting place.

Aristotelian thought forces the cross into an alien frame of meaning, which it is not allowed to critique. Something else becomes the ultimate criterion of theology, through which the cross is interpreted.

The cross mounts a full-scale assault on human preconceptions of God. A theology of glory prioritizes the rational, what the human mind can cope with. The theology of the cross instead observes what is seen and deals with those realities. “Only experience makes a theologian.”

The cross reveals the truth about the world. A theology of the cross stands against any kind of intellectual speculation about the nature of things. The cross reveals how a Christian is to live in the dark wastelands of this fallen world. We must allow its pain suffering in silence to impact us.

“We simply cannot be allowed to sanitize or domesticate the brutality and horror of the cross in our headlong rush to extract some abstract, sanitized theological principles from the historical carnage and brutality of Good Friday.”

McGrath points out the theology of the cross is not an atonement theology. It is a compass rather than a map.

The reality of the situation is that human beings are simultaneously both sinners and justified. The cross of Christ, God’s wrath and God’s mercy are revealed simultaneously. That may be rationally implausible, and theologically messy, but that is the truth of the situation.

God’s self-disclosure is in the suffering and death of the cross rather than in human moral activity. This knowledge of God, hidden in his revelation, is a matter of faith. Faith alone recognizes the self-disclosure of the Posteriora Dei.  Philip asked Jesus to show him the Father, which makes him a theologian of glory according to Luther. Jesus says, “Whoever has seen me has seen the Father.”  Isaiah says, “Truly, you are a hidden God.”

God is particularly known through suffering. This was current Augustinian theology.

All of this is consistent with Paul’s teaching about the foolishness of the cross. The unbeliever looks upon the cross and sees only the helplessness and hopelessness of an abandoned man dying on the cross. The theologian of the cross recognizes the veiled but real activity of the hidden God.

The theology of the cross is a radical critique of the analogy of human justice with divine justice, human righteousness with divine righteousness. This parallels the emerging dialectical theology of the early 20th century. Any attempt to see God outside the cross of Christ is idle speculation. God’s strength is revealed weakness. God’s wisdom through folly.

There are a lot of books out on Luther studies these days, as we approach the 500th anniversary of the Reformation in 1517. Add this work of detailed scholarship by an Oxford University professor to your list.