Hugo de Groot (1583-1645) is internationally known as the father of international law and also celebrated for his seminal work on the law of nature. The principal work of Johannes Voet (1647-1713) is his Commentarius ad Pandectas in which he expounds the modern law (the jus hodiernum) in the light of the Pandects of Roman law. In the first title of his Commentary, Voet briefly sets out his views on the foundations of natural law. He rejects the views of De Groot on this score as unacceptable. The purpose of this note is to trace the exposure of De Groot and Voet to the subtleties of the esoteric theological debates in Reformed (Calvinist) circles in seventeenth century Holland, and to highlight the theological background to their differing views on the source of the law of nature.