Carmichael argues that Johannes Cocceius's theology of the Sabbath serves as a window through which one can view more clearly his federal theology or covenant theology. Covenant theology was the most distinctive feature of his theology. Moreover, Cocceius spent a notable portion of his life engaging in the Leiden Sabbath Controversies from 1655 to 1659, which played a key role in the split of the Reformed Dutch Republic into two socio-political blocs—Cocceians and Voetians. So far scholars have tended to overlook this critical phase in Cocceius's theological development. Carmichael sheds light on it by looking at the theological texts that Cocceius wrote that absorbed his attention during this significant period. Casey Carmichael examines first the evolution of the problem of the Sabbath in Cocceius's theological tradition—Reformed Orthodoxy—in Chapters 2–4 and second the development of Cocceius's doctrine of the Sabbath, structured around the Leiden Sabbath Controversies, in Chapters 5–8.