According to Calvin, all discussions of the office of magistrates, the making of laws, and public welfare begins with religion and divine worship and therefore piety is the first concern that no government and its laws are worthy of its salt which neglects God’s right and provide only for men.
According to Calvin, among philosophers of all nations, religion takes first place. So in places where Christians and magistrates do not apply religion they are in error. In which case such duty is part of their duties assigned by God. So they have to ensure that it is protected.
In scriptures, kings who followed God and restored the worship of God when it was corrupted were greatly praised. For those who did not, most were cursed.
To Calvin, some kings behaved as if God appointed rulers in his name to decide earthly things but overlooked what was of far greater importance – that he himself should be purely worshiped according to the prescription of his laws.
Men develop passion to alter everything with impunity which drives turbulent men to the point of wanting all vindicators of violated piety removed from their midst. Prophets admonish kings to “do justice and righteousness” to deliver to him who has been oppressed by force from the hand of the oppressor.” According to the psalmist, they are also to give justice to the poor and needy, and deliver the poor and needy from the hand of the oppressor.
Mosses commanded his leaders to “hear cases between their brethren and judge…”
To Calvin, kings should not multiply horses for themselves, nor set their minds upon avarice; nor be lifted up above their brethren. Kings should be constant in meditating upon the law of the Lord all the days of their life.
According to Calvin, magistrates are ordained protectors and vindicators of public innocence, modesty, decency, and tranquility, and that their sole endeavor should be to provide for the common safety and peace of all. They cannot perform this unless they defend good men from wrongs and the wicked, and give aid and protection to the oppressed. They also have the power with which they severely coerce the open malefactors and criminals by whose wickedness the public peace is disturbed.