Calvin's Defense of Politics

Institutes of the Christian Religion
Book IV, Chap. XX

  1. Objections of the Anabaptists,
    1. That civil government is unworthy of a Christian man.
    2. That it is diametrically repugnant to the Christian profession. Answer.

Calvin's Institutes (pink column)
Our analysis (green column)
2. The two "governments" are not antithetical 

Still the distinction does not go so far as to justify us in supposing that the whole scheme of civil government is matter of pollution, with which Christian men have nothing to do. Fanatics, indeed delighting in unbridled license, insist and vociferate that after we are dead by Christ to the elements of this world, and being translated into the kingdom of God sit among the celestial, it is unworthy of us, and far beneath our dignity to be occupied with those profane and impure cares which relate to matters alien from a Christian man. 

To what ends they say, are laws without courts and tribunals? But what has a Christian man to do with courts? Nay, if it is unlawful to kill, what have we to do with laws and courts? 
There is in fact a powerful argument here, but misapplied. Paul warns believers against taking their disputes before secular courts (1 Corinthians 6:1-11). But this does not mean less involvement in the resolution of disputes; it means more. Details here.
But as we lately taught that that kind of government is distinct from the spiritual and inward kingdom of Christ, so we ought to know that they are not adverse to each other. 
It is dangerous and neo-platonic to consider the Kingdom of God as being only "spiritual and inward." God's Reign and His Law claim jurisdiction over our businesses, schools, homes, voluntary associations -- in short, over everything where the State claims jurisdiction. No area of life and action is outside the Kingdom and its Law.
The Kingdom may be said to be a broader concept than the Church, because it aims at nothing less than the complete control of all the manifestations of life. It represents the dominion of God in every sphere of human endeavor.
Louis Berkhof, Systematic Theology, Eerdmans, 1946, p. 570
The former, in some measure, begins the heavenly kingdom in us, even now upon earth, and in this mortal and evanescent life commences immortal and incorruptible blessedness, 
It is correct to see that God's will should be done now, on earth, "as it is in heaven." 
while to the latter it is assigned, so long as we live among men, 
1. to foster and maintain the external worship of God, 
2. to defend sound doctrine and the condition of the Church,  
Calvin, along with the "magisterial reformers," and the Second Reformation believed that the State had the duty to involve itself in the worship of the Church. Only a few churches still believe this. Not only do most churches believe in the "separation of church and state" . . .
3. to adapt our conduct to human society, 
4. to form our manners to civil justice,  
. . . they also believe in the separation of school and state. At least they would say the believe in the separation of culture and state. Calvin believed the State also had a duty to educate. It is clear that education is a central foundation of social order. If parents undertook education as a divine responsibility, many of the social ills from which the State promises to protect us would not exist. More here.
5. to conciliate us to each other, 
6. to cherish common peace and tranquillity. 
Internationally, there is probably no greater source of division in the world than the nation-state. In the U.S. domestically, the federal government encourages class-war and racial conflict, as well as conflicts between Christians and anti-Christian groups (such as abortionists and homosexuals) by its use of taxpayer-funded "entitlements." If an optimistic visionary can imagine the State "conciliating us to each other," that same creative energy might be better employed visualizing the church teaching the principles of conciliation and seeing those principles embodied in families and voluntary associations.
All these I confess to be superfluous, if the kingdom of God, as it now exists within us, extinguishes the present life. But if it is the will of God that while we aspire to true piety we are pilgrims upon the earth, and if such pilgrimage stands in need of such aids, those who take them away from man rob him of his humanity.
The question (unanswered by Calvin) is whether the State is the only or even the best provider of "such aids" to conciliation and social order.
 As to their allegation, that there ought to be such perfection in the Church of God that her guidance should suffice for law, they stupidly imagine her to be such as she never can he found in the community of men.
Why is it easier to imagine the purity and morality of the State's conciliatory activities than of the Church's? As a matter of historical fact, it has been the Church (the Body of Believers) that has been salt and light and has preserved culture and social order, to a greater extent than the State. Consider the impact of the Church during America's revolution. It should be even greater.
For while the insolence of the wicked is so great, and their iniquity so stubborn, that it can scarcely be curbed by any severity of laws, what do we expect would be done by those whom force can scarcely repress from doing ill, were they to see perfect impunity for their wickedness?
Calvin is no longer talking about conciliation and cultivation of manners, but about brute force and vengeance. It is assumed that if there were no State, there would be no sanctions against evil; that businesses and schools, landlords and family members, would never do anything to chastise criminal behavior. Nobody would ever be fired, flunked, evicted or disinherited. But if an insurance company would not raise the rates of someone who commits a crime, why would the agents of the insurance company vote for politicians who would punish bad behavior? If consumers would not boycott, and business owners would continue to serve, those who disrupt social order, why would they elect government officials who were committed to doing anything different? If the people can be trusted with the vote, they can be trusted to implement decentralized sanctions in their own lives which would permeate society. Crime exists today not because the government is too soft on crime, but because businesses, schools, landlords, insurance companies, families and the media are all soft on rudeness and disrespect, theft and poor performance, promiscuity and "date-rape," violence and even murder. It is society as a whole, not just "the government," that must send moral messages and reinforce behavior through myriad sanctions.