Book excerpt: Rabbi Moses Hagiz, one of the most prominent and influential Jewish leaders of seventeenth-century Amsterdam, devoted his career to restoring rabbinic authority. His most prominent talent was as a polemicist, and he campaigned ceaselessly against Jewish heresy in an attempt to unify the rabbinate. During Hagiz's lifetime there was an overall decline in rabbinic authority, which the author argues was the result of migration and assimilation.