During the mid-seventeenth century, Anglo-American Protestants described Native American ceremonies as savage devilry, Islamic teaching as violent chicanery, and Catholicism as repugnant superstition. By the mid-eighteenth century, they would describe amicable debates between evangelical missionaries and Algonquian religious leaders about the moral appeal of Christianity, recount learned conversations between English merchants and Muslim scholars, and tell of encounters with hospitable and sincere priests in Catholic Canada and Europe. What explains this poignant shift?

Using a variety of sources, The Opening of the Protestant Mind traces a transformation in how English and colonial American Protestants described other religions during a crucial period of English colonization of North America. After the English Revolution of 1688 and the subsequent growth of the British empire, observers began to link Britain's success to civic moral virtues, including religious toleration, rather than to any particular religious creed. Mark Valeri shows how a wide range of Protestants—including liberal Anglicans, Calvinist dissenters, deists, and evangelicals—began to see other religions not as entirely good or entirely bad, but as complex, and to evaluate them according to their commitment to religious liberty.