Anabaptists are not actually Protestants. One question divides Protestants and Anabaptists: Is the visible Church on earth to contain both true believers and false, both wheat and tares? Conversely, is every true assembly of the Church composed purely of the wheat?
Protestants answer yes to the first question and no to the second; Anabaptists do the opposite. Anabaptists, unlike Protestants, didn’t seek to reform the existing visible Church (since the invisible Church cannot be reformed by man at all, being the realm of the human soul, which none rule but God); instead they sought to make, from the number of ‘new’ believers leaving the old corrupt Church, a new, different, separate ‘pure’ Church, living apart from ‘the world’. Because the Anabaptists saw the Church of Rome not only as the seat of the papal Antichrist (as the Protestants viewed it as well) but also as a completely false Church, and irredeemable, the only way was to separate from and shun this worldly institution to gather into a new, godly community. Since the baptism of the world was invalid, the symbol of this new community of ‘true believers’ was rebaptism into voluntary membership in this new community, a baptism predicated on walking in newness of life.
The two kingdoms, and nature and grace
This difference in theory is the Protestant doctrine of the two kingdoms. This doctrine, developed out of older Catholic theories of the Church, is the way in which Protestants can teach justification by faith alone. It teaches that God is the ruler of the whole world and that he rules in two ways. The earthly kingdom, or the left-hand, he rules through temporal government, by means of law (i.e., the sword or compulsion); the heavenly kingdom, or the right-hand, he rules by the Holy Ghost, through the gospel of grace. To the latter kingdom, the spiritual, belong Christians as a new creation that voluntarily obeys; to the former belong all who live on earth, including Christians.
Anabaptists have no doctrine of the two kingdoms. Therefore, since true believers in the Anabaptist order didn’t live within the same polis as the non-believers, Christians could not serve in civil governments or swear oaths in their courts. Nor was the magistrate’s sword to be coöperated with, since it belonged to the world and lay outside the people of God. God’s elect were instead to use excommunication, or the ban, to exclude sinners from the company of both God and his people; to be in the world and apart from God’s people was to be in the company of the damned. In short, Christians could have no rule on earth but ‘Scripture itself’.
The idea was a radical doctrine of sola Scriptura with no use for natural law or anything but the illumination of the Holy Ghost, which being spiritual had nothing to do with the natural. This idea contrasted with the Protestant sola Scriptura: that the Holy Scriptures reveal all things necessary for eternal salvation through faith in Jesus Christ, and the dogmas added to them by the Pope cannot damn anyone. The classical Protestant doctrine is what Richard Hooker taught in Lawes of Ecclesiastical Politie against the both papalists and the disciplinarian biblicists (such as Thomas Cartwright):
The schooles of Rome teach scripture to be so unsufficient, as if, except traditions were added, it did not conteine all revealed and supernaturall truth, which absolutely is necessarie for the children of men in this life to know that they may be in the next saved. Others justly condemning this opinion growe likewise unto a daungerous extremitie, as if scripture did not onely containe all thinges in that kinde necessary, but al thinges simply, and in such sorte that to doe any thing according to any other lawe were not onely unnecessary, but even opposite unto salvation, unlawfull and sunful.
The Anabaptists’ version of sola Scriptura, against that of Hooker and the Reformers, has resulted in aberrant behaviours, which I outline below.
Results of Anabaptist theology
Some Anabaptists rejected the sword altogether; others, such as the Münsterites, took up arms against ‘the world’. Radical Puritans like Cartwright, by similar reasoning about Holy Scripture, admitted to public worship only the things that the Scriptures expressly called for, concluding, ‘Scripture is the onely rule of all things which in this life may be done by men.’ Like the Romanists, ironically, these groups at the logical extremes subordinated the ‘natural end’ of man to his ‘supernatural end’ (cf. Boniface VIII’s papal bull Unam Sanctam, which subjects all Christian kings to the Bishop of Rome). The fruit of the Anabaptists’ stolid biblicism is dissension and sedition, and all kinds of evils in the Church (as for the Romanists, ‘remember, remember the fifth of November’).
Another result in our own time, transfigured by theologically liberal tendencies, is an extreme resistance to any call to do things lawfully in the Church. The Anabaptist perception of the legal system as inherently pagan, or at least as (rightly or wrongly) impervious to the word of God, makes people reluctant to mix church and law at all, either in excommunication or in ‘legalistic’ reporting to the magistrates; thinking that a ‘system of grace’ means no law, no rigorous thought and no clear distinctions between being morally wrong and doing unpopular, uncomfortable things (unless with pastoral approval), Christians are often uneasy even with the term government when I refer to the government of such and such a church. Insistence on informal ‘leadership’ and resistance to formal procedures has perhaps hurt Sovereign Grace Ministries at a time when formal canon law might really have helped.
As common in our time, if not more common, is a sacred-secular divide, under which things not obviously spiritual (which pertain to ‘the culture’ and not to evangelism) are either condemned as unspiritual or permissively lumped together with truly unholy things as ‘what does not belong to God’. But what truly doesn’t belong to God? Falsity and wickedness and corruption, which don’t condemn a good thing but are themselves condemned, for God cannot sin, nor can he lie, nor can he tempt a man to sin. Christ is the truth, and evil is the lie; those who cling to Christ will have all good, but those who cling to evil are black as sin in God’s sight, and they will with sin be burned in everlasting fire. At the end of the age, the chaff will be burnt up, and the wheat will grow thick and rich in the new heavens and the new earth, and man will forever live in blessed joy.
Related books, recommended by Kenny Robertson:
Creation Regained, by Albert M. Wolters (Eerdmans);
Maximum Life, by Julian Hardyman (IVP).
Cogito, Credo, Petam 
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