Moses the God of Aaron, or the Power and Duty of Princes in Sacred Matters

...ought to lead, not only as a man, but also, and indeed much more, insofar as he is a Prince Princeps: the sovereign or supreme ruler of a state. But if indeed it were said that this duty is unknown by natural law jus naturæ: a system of law based on human reason and the inherent nature of the world, rather than specific religious revelation, as some contend, nevertheless such a Prince is obligated to it because of the mandate of God revealed in Scripture. This is because, once the way of eternal salvation is known, he both can and ought to recognize it.

Nor, however, does it follow from this that the Christian religion brings any change to the rights of Majesty original: "juribus Majestatis"; the supreme powers and legal privileges inherent to a sovereign. For God, by this new precept—if indeed it were new—commanded nothing contrary to natural law. Instead, He at least added a new obligation to it, which He was able to do by the same authority by which He prescribed natural law itself and universal positive laws man-made laws established by a government or ruler even to Princes. In the meantime, the royal rights jura regalia: the specific powers and rights belonging to a monarch by virtue of their office which belong to a Prince by natural law remain preserved; they are neither removed nor diminished by this reasoning.

Rather, royal rights are confirmed through revealed religion. For Samuel repeated the "right of the King" original: "jus Regis"; referring to the description of monarchical power in 1 Samuel 8—as it is called by the Holy Spirit Himself—to deter the Israelites from their purpose. This is a right a King possesses not only when he is first appointed or at the start of his royal duties, but also once he is established throughout his entire reign. This is clear to anyone looking at specific examples in 1 Samuel 8:9–17 and Romans 13:6–7.

To ensure he uses this right correctly and prudently, he is cautioned by God in Deuteronomy 17:16–20. Therefore, the Christian religion brings no change to the rights of majesty.