Benjamin Kaplan’s Divided By Faith is primarily a revisionist history of the rise of toleration in early modern Europe. He challenges the Enlightenment notion that 18th-century intellectuals introduced the idea, showing instead that toleration appeared first as a set of practices in religiously diverse regions of Europe and was first expressed theoretically from within the church.

At the outset, though, he tells a tale of intolerance, starting, predictably, with Servetus in Geneva, but arguing, less predictably, that the intolerance of the Reformation era was fed by the movement historians have come to call “confessionalization.” 

Preachers and writers identified themselves through oppositions and contrasts. The church of England, home to everyone from Perkins to Laud, was united by “a pervasive and virulent anti-Catholicism.” Anglicans could live together with their liturgical, governmental, and doctrinal differences because they were united against common enemies - “the bloodthirsty inquisitor, the Jesuit spy, the tyrannical prince, the traitor who gave his allegiance to Rome” (37). That such anti-Catholic fantasies happened to bolster the power of state-building monarchs was not incidental.

With the crypto-Calvinist struggles in Lutheran churches, Protestants adopted a via negativa toward one another: “Out of the crypto-Calvinist controversy . .  . emerged a more precise and rigid definition of Lutheran orthodoxy. Those who did not concur with it were disciplined into conformity or expelled from the Lutheran churches, while within those churches beliefs and practices grew more uniform” (42). Reformed churches, aiming to “abolish everything that smacked of Catholicism,” make their specific practices “markers of confessional identity” (41). Practices that were originally treated as adiaphora were fixed.