Where Erasmus had found it necessary to flee from monastic life, Luther fled to it, against his father’s wishes. But even within the monastery, his Anfechtungen continued. How could one know that all one’s pious efforts would be judged adequate in the eyes of God? He eventually found his answer, gleaned from his reading of Paul’s Epistle to the Romans: We need not worry about failing, since nothing we do makes any difference. Our fate is predestined by God, and our salvation will come through faith in that conviction. Luther’s famous principle of “justification by faith,” making (some of) us passive recipients of God’s unearned love, would become central in the movement that would eventually be known as Protestantism.

For Luther, nothing he didn’t personally hear reverberating within the words of Scripture could be sanctioned, including the vast hierarchy of the church and its self-serving dictums. Erasmus’s declaration (in his “Enchiridion”) that “monasticism is not piety” resonated with him. He also used Erasmus’s New Testament (the second of the five editions it would undergo) for his own translation of Scripture into German, so that the people themselves might take their religion directly from that one true source. “All Christians are priests,” Luther provocatively wrote.

Into that narrow space of questioning the church’s authority that Erasmus had pried apart, Luther stepped, and blasted it wide open. Erasmus was horrified — horrified at the violence of Luther’s certitude, horrified at the violence his certitude bred within Christendom. Erasmus was among the earliest of pacifists, calling Mars “the stupidest of all the gods,” so there is a tragic irony in his having contributed, no matter how indirectly, to the bloody sectarian turmoil that erupted from Christianity’s splintering.

In his divergence from Luther, Erasmus is often viewed as the one at a disadvantage. Whereas Luther displayed the courage of his convictions, Erasmus comes off as a self-protective pragmatist, seeking accommodation with the church so as to pursue his life with a minimum of upset. Little suggests otherwise in “Fatal Discord,” and that is regrettable. In the dialogue between Luther and Erasmus, Massing has omitted Erasmus’s strongest lines, which are epistemological in nature. Erasmus doubts Luther’s absolute rule of faith more than he doubts the institution of the church, whose flaws — he hoped — could be corrected. He is justifiably skeptical of a self-verifying criterion for truth that can generate the kind of knowledge Luther claimed for himself. This principled skepticism is the epistemological backbone that stiffened his anti-Lutheran stance.

Massing writes that Erasmus’s influences on us today, unlike Luther’s, are faint. I disagree. Modern philosophy was born in the century after Erasmus and Luther. It emerged, not coincidentally, in the wake of the ensanguined doctrinal disputes that killed off Europeans at a higher percentage of their population than did World War I. Modern philosophy would be marked by its refocus on epistemology, which scrupulously analyzes the conditions for knowledge, as opposed to mere belief, and which recognizes, in the spirit of Erasmus, that among the threats to human flourishing, we should not underestimate the dangers of misplaced certitude.