MOSES MAIMONIDES was the most eminent authority of rabbinic law and Jewish thought in the medieval Jewish world, proficient in all its canonical sources up to his time. In a broader sense, he was also a master of the scientific/philosophical corpus of his day, as demonstrated not only by his writings, but by his rise to a position of official physician at Saladin's royal court in Egypt. As a result, what he had to say on matters crucial to Jewish existence and the practice of Judaism has seminally influenced the evolution of Jewish thought, worship, and observance ever since. Without this potent combination of both rabbinic expertise and philosophical acumen, Maimonides could easily have been ignored by devotees of either school, and thus would not loom as large over the development of Jewish thought as he does, or indeed even be the subject of the present book. Maimonides was the quintessential Jewish sage, at home in all rabbinic disciplines. He perfectly fits the rabbinic model of the talmid ḥakham (scholar) who is ‘proficient in Bible, Mishnah, Talmud, halakhot, and agadot’.

He augmented—or, as Menachem Kellner describes it, encumbered— Judaism with the Thirteen Principles of faith, a pioneering fundamental credo which quickly became sacrosanct. Despite a long history of scepticism towards its authoritativeness by the elites of rabbinic law, it is still safe to characterize it as having achieved canonical status in Judaism. He also compiled the first comprehensive code of Jewish law in the history of Judaism. Though Joseph Karo's Shulḥan arukh superseded its practical authority from the sixteenth century on, Maimonides’ Mishneh torah nevertheless became the third prong of the rabbinic academic canon, alongside the Hebrew Bible and the Talmud. Joseph Karo indeed thought of himself as a successor to Maimonides, whom he considered the most central and authoritative figure in halakhah even centuries after his death.

The Rambam of the Mishneh torah was canonized almost immediately. His slightly older contemporary, Rabad (Rabbi Abraham ben David of Posquières, c.1125–1198), wrote a series of caustic glosses on the work during Maimonides’ lifetime. While people often focus on the criticisms in the glosses, the fact that an authority of Rabad's stature saw fit to write them shows clearly how important he thought the book was.