Alright then, on postmill assumptions, knowing that there will come a time when they will not hurt nor destroy in all God's holy mountain, when will we know to shut down all the fire departments? This is not a trick question. Actually, if you think about it, it might be a trick question.
We will know to shut down all the fire departments when houses stop burning down. When we have perfected fire retardant construction materials, say, and we haven't had a fire in this town for a hundred years, there will come a time when those who want to keep the fire department on the city budget for nostalgic reasons will finally lose the argument. In short, fire departments will disappear when fires do.
And in the same way, police departments will not be necessary when there is no more crime, and armies and navies will not be necessary when nations stop threatening one another.
I use the phrase "postmill assumptions" because this is actually an important aspect to understanding the teaching of Paul on the civil authority in Romans 13. As I am fond of saying, there is a ditch on both sides of the road. For the pacifists and quasi-pacifists, the eschaton is now, or ought to be, and the Incarnation of Jesus is seen as the signal to begin disarming now, and we are already two thousand years behind schedule. In this view, Romans 13, which gives the diaconal sword to the magistrate, is a real inconvenience, and is frequently dismissed as a temporary arrangement, or as saying far less than it actually says. On the other hand, there is the static view of the relationship of human history to human evil (premill and amill), which says that magistrates needed to be banging heads together two thousand years ago, and will no doubt be needing to be banging heads together in just the same way two thousand years from now. If the Lord tarries, a premill brother might add.
The postmill thinker has a different view of history, and so when it comes to the era of peace for this world that he believes is coming before the Second Coming, he has to answer questions about development, pace, preconditions, and so forth. In Paul's day, Roman justice was rough, pretty grim, and yet comparatively fair. In fact, the Romans had a better grip on certain principles of justice than do certain Internet doctrine jockies. "To whom I answered, It is not the manner of the Romans to deliver any man to die, before that he which is accused have the accusers face to face, and have licence to answer for himself concerning the crime laid against him" (Acts 25:16). At the same time, it was clear evidence that Paul was no perfectionist when he labeled Nero as God's deacon of justice . . . even during the time when Seneca had his foot on the brake.
But the postmill view of history does not anticipate having to call a long series of future Neros "God's deacon." We are laboring for the elimination of rough justice in the hands of thugs in favor of refined and surgical justice in the hands of godly men. And over time, those godly men will have less and less to do. How much time? Actually, quite a lot.
During this time, the magistrate becomes more just, not less, and this justice includes punishing the wrong-doer, the task that God has assigned to the magistrate. Now this view is only legitimate just so long as there are wrong-doers to punish. If, through the influence of the gospel, the crime rate drops to zero, but we still have cops arresting and charging people with antique crimes just so the police department will not have to lay anybody off, then something is seriously screwed up. In fact, it would be so screwed up as to constitute an officially-sanctioned crime, which should be restrained by force from other quarters, meaning that we are not quite there yet. When we are there, and we don't study war any more, or riot control tactics, or SWAT team maneuvers, it will be because we don't need to anymore. And the the fact we don't need to anymore will be glaringly obvious.
This means that the postmill view of Romans 13 is realistic, just like the premill and amill views are. We do not advocate the dismantling of our coercive institutions until there are no more rapes and murders. We do not advocate the dismantling of our militaries until invasions are truly impossible. At the same time, the postmill view of Romans 13 expects transformations in how that passage will be applied, just as the pacifists and quasi-pacifists urge. We just don't await those transformations impatiently. The pacifist is to be commended for his idealism, but not for his dreamy detachment from the real world as it actually works. The premill and amill thinkers are to be commended for their realism and recognition of the gritty facts on the ground, but not for their de facto neglect of what the coming of Christ is supposed to mean in the transformation of this history of ours. That leaves the postmill position to reconcile these two elements, and though it may be a coincidence, that is the position I hold.
Having said all this, it is important to set the stage for a detailed treatment of Romans 13. Let this serve as a key introduction, with the details to come later.
In Romans 12, the apostle tells these Roman Christians to swear off personal vengeance. This is not because vengeance is wrong, but rather because vengeance is God's (Rom. 12:19). The Christian who does not take personal vengeance is told to forswear this by making room for wrath, by stepping aside so that wrath may come. If someone wrongs you grievously, then feed him when he is hungry and give him something to drink when he is thirsty (Rom. 12:20). This is how to overcome evil with good -- extend personal kindness while leaving room for God's wrath.
But in context, what is that wrath? We need to remember that when Romans was written, it was not divided up into chapters and verses. The section immediately following this is the place where Paul tells us that the magistrate is God's deacon of wrath (Rom. 13:4). God has deputized the civil magistrate, and has given him the authority to use the sword on those who do evil. When he does so, he is visiting God's wrath on the criminal, and it is this wrath that the Christian is commanded to leave room for.
Again, we are confronted with two errors of excess, and we find that the balanced biblical position is the one that holds to the truth articulated by each of these positions, but which also holds to the truth that each one neglects. The pacifist believes that he can extend personal kindness without stepping aside for God's wrath as embodied in the civil magistrate. The "hang 'em high" justice-monger believes that he can use the civil magistrate as a surrogate in his own desire for personal vengeance, and he ignores what the Bible bluntly and plainly says about the need for personal grace and kindness extended to the one who has done evil to him.
But each of these options is disobedience, and ironically, they are exactly the same kind of "picking and choosing" disobedience. Paul says that when you are horribly wronged you are to do two things, not one thing -- extend personal grace and call the cops. But the law and order guy calls the cops, swearing under his breath about the "damn kids these days," and the moonbeam sentimentalist strews flowers and forgiveness in every direction -- and expresses ten times more disapproval for the police who recovered his car than he does for the drunk teenagers who stole it.
A man in the flesh can easily do either one of these things. Only a man in the Spirit can do both.