Many Jewish groups of late antiquity assumed that they were obligated to observe the Divine Law. This book attempts to study the various rationales offered by these groups to explain the authority that the Divine Law had over them. Second Temple groups tended to look towards philosophy or metaphysics to justify the Divine Law's authority. The tannaim, though, formulated legal arguments that obligate Israel to observe the Divine Law. While this turn towards legalism is pan-tannaitic, two distinct legal arguments can be identified in tannaitic literature. These specific arguments about the Divine Law's authority, link to a set of issues regarding the tannaim's conception of Divine Law and of Israel's election.