Before examining the Catholic Church’s relationship with the Jews in the Middle Ages, it would be worthwhile to state an obvious yet often overlooked fact: The Middle Ages were, well, medieval. In a modern, post-Enlightenment world, religious belief is merely a personal preference, like a favorite color. But in most premodern civilizations, religion is a central, if not predominant, aspect of one’s personal and collective identity. To seek to corrupt or defame a culture’s religion would therefore be the equivalent of treason in the modern era. In both cases the crimes were thought to be severe enough to warrant the...