Edit: Since writing this, I have become more familiar with the different groups who claim the name "Theonomy". It seems to me that most modern critiques of Theonomy have a Bahnsenian or Rushdoonian idea of Theonomy in mind, though these are not widely held by many today. I don't think this position is coherent and I think it deviates from the Westminster Confession. Doug Wilson's version of what he calls general-equity theonomy, however, it seems to me just is the Reformed view. My critique here applies primarily to the Bahnsen/Rushdoony view, however, it can also be applied to Wilson's in that he still believes that it is the church's duty to bring in the Kingdom of God in civil society, which is really essential to Postmillennialism itself more so than it is to theonomy in particular. I think my argument still holds true then, as it seems to me that Postmillennialism must give way to a form of One-Kingdom Theology regardless of the adherent. Were Wilson an amillennialist, I think his version of general equity theonomy would be perfectly in line with 2K theology.
I have recently been reading Sam Renihan’s published dissertation, “From Shadow to Substance”, after doing a deep-dive on baptismal regeneration and seeing how infant baptism was so tied both to the theology of baptismal regeneration as well as the mixing of church and state into a political theocracy throughout church history (and, consequently, the denial of the perseverance of the saints). So the issues of ecclesiology and covenant theology are fresh in my mind right now. However, for the first time it has crossed my mind that a distinctly Baptist covenant theology should be tied directly to amillennialism, as it makes an implicity argument against chiliasm both in its premillennial and postmillennial form. I have never seen anyone make this argument, however, I hope to here suggest that a Baptist view of the New Covenant (and hence, ecclesiology), implicitly rules out chiliasm on the basis of the fact that God governs His kingdoms through covenant. Once I started thinking about this, I realized this was actually a pretty obvious logical conclusion, so I hope you can see where I’m going with this.
I'm convinced that a great amount of the errors throughout Church history up until today are caused by a faulty ecclesiology; namely, what the the Church actually is, according to, and as defined by, the New Covenant. The wide-ranging extent of the argument from a proper understanding of the New Covenant has been amazing to me. Stephen Wellum has grasped the argument masterfully and used it to argue against both infant baptism in "Believer's Baptism" and against unlimited atonement in "From Heaven He Came and Sought Her", in two of the most excellent theological chapters I have ever read. And of course, it's been used by numerous writers to argue for the perseverance of the saints. A proper understanding of the New Covenant is so powerful that it does away with Presbyterians, Arminians, Roman Catholics, Anglicans, Lutherans, and the Eastern Orthodox all at the same time. However, I want to suggest that we can go even further than this and see that it does away with chiliasm as well.**
In amillennialism alone is the scope of the mediatorial equivalent with the scope of the millennial kingdom
Put simply, a Baptist ecclesiology views the people of the Kingdom of God to be entirely regenerate. To be a part of the New Covenant is to be regenerate, and to be regenerate is to be a part of the New Covenant. There is no “external” part of the New Covenant. It is entirely internal.
In contrast, the paedobaptist view of the New Covenant (and hence, the Church) conceives of an external administration that consists of unregenerate children of believers. It is not hard to see how infant baptism led to a theocratic-political mixing of church and state in the Middle Ages and on into the Reformation in this regard. In my view, The Federal Vision and people like Doug Wilson are simply trying to take the theology of Westminster to its logical conclusion. For that reason, when I refer to “postmillennialism” here, I am referring to the kind taught by Wilson, Gentry, DeMar, Bahnsen, etc., which I believe is rightly consistently connected to theonomy by those who espouse this theological system. The Great Commission takes on a political-civil element in this system. The goal of the millennium here is to establish God’s kingdom on Earth, and this consists of political elements, as it consists in the baptism of unregenerate children who will participate in this kingdom.
The premillennialist does not actually have too much of a different view of the substance of the millennial kingdom in comparison to the Wilsonite postmillennialist. He does not believe the kingdom will be established through the spread of the Gospel of Christ and the baptism of children into the covenant like the Wilsonite. Rather, he believes Christ will come from Heaven to Earth and establish this earthly reign. Yet, he still believes this kingdom reign will be a reign of Christ over both the regenerate and the unregenerate and that this will certainly involve political elements.
What is the similarity between the postmillennialist and the premillennialist? It is that they both believe that Christ’s Kingdom rule does (or will) extend to the unregenerate. Yet, it is the clear teaching of the Bible that God governs his Kingdoms through covenant (see Sam Renihan’s “The Mystery of Christ” for this). The Kingdom of Creation is governed through the Adamic and Noahic covenants. The Kingdom of Israel was governed through the Abrahamic, Mosaic, and Davidic covenants. And the Kingdom of Christ is governed through the New Covenant. But, the biblical-theological argument I am making here is that the New Covenant is not like the Old Israelite covenant.
The earthly political kingdom of Israel was only typal of the heavenly Kingdom of Christ. Therefore, we cannot determine the nature of Christ's millennial reign by making a one-to-one comparison to the Israelite kingdom, but we must first consider how the foundational nature of the Kingdom of Christ differs from it. It does not consist of external elements. The Kingdom is Christ is delimited by the New Covenant, and the New Covenant consists only in those who are regenerate. What this means is that it is a mistake to see Christ’s millennial reign as consisting in political and external elements; for it is a mistake to see Christ’s reign as in any way at all being a reign over the unregenerate.
The Kingdom of Christ is established by the New Covenant, and it is the New Covenant that determines the parameters of that reign. There is an “already” and a “not yet” to Christ’s reign, but the “not yet” can never be of a completely different substance than the “already” (thus, for example, the premillennialist cannot have an “already” spiritual reign of Christ now over believers, then a “not yet” of a political reign over believers and non-believers in the millennial kingdom, and finally a further “not yet” over just believers again on the New Earth). The New Covenant will simply not allow it because Christ’s Kingdom is not of this world (this is, of course, not to say that the Kingdom will not come to this earth, as I said, there is a "not yet", but that when it does, it must only be in the New Earth which will not consist of unbelievers; thus during Christ's reign there "will not be a Canaanite in the house of the Lord", Zech. 14:21). The nature of Christ’s reign, as determined by the New Covenant, is such that it knows nothing of the reign of Christ over the unregenerate because it does not allow of political/external elements. It is not those who are of the flesh who can/will participate in the reign of Christ’s Kingdom, but it is only those who are of the Spirit who ever can or will. Chiliasm thus ends up failing because it is bad biblical theology that fails to connect a proper ecclesiology to eschatology.
In other words, in order to determine the nature of the millennial reign, we first have to step back and ask ourselves a more fundamental question: "what is the nature of Christ's Kingdom?". It is the New Covenant that defines who the participants in the reign of Christ are. Therefore in order to come to a correct conclusion about the reign of Christ, we must first come to the proper conclusion about the nature of the New Covenant.
I am sure that chiliasts would have many different objections to my argument, and I by no means have tried to fully develop it here, but I am absolutely confident in it when we look at the nature of biblical-theology and the function of covenants in God's rule in the biblical storyline. Both Progressive Covenantalists and 1689 Federalists could adopt my argument here (as I think they should), but I only mean here to present the argument, as I have not yet seen it made before by others.
* I just want to say that I am not very familiar with the theonomic postmillennial eschatology (or any postmillennial eschatology for that matter). However, I do think the general argument here still holds, even if I haven't accurately and precisely put it. My deepest apologies for any misrepresentation especially towards theonomists, whom I have found so often misrepresented and whom I share many common concerns with.
** I also want to point out this is a similar argument with justification, where everyone without a Calvinist soteriology logically falls into works-righteousness because it is ultimately on you to maintain your justification (and not in the sense of perseverance through works, but by works which take on a meritorious character in order to remain justified…i.e. one can fail to remain justified due to their own sin). You get in by grace, but you stay in by works (yes, these works are done out of grace, but that was never Paul's argument. [Edit A condition is put on the *right to eternal life* rather than simply a condition on the continuous possession of eternal life. In other words, justification gives you the right to eternal life, which includes perseverance in it. The perseverance is a necessary condition, but under a view where perseverance can be lost, the right to it must necessarily be taken away. Therefore the right to eternal life (justification) becomes conditioned upon what one does. This creates a new covenant of works.] The Pharisee who prayed "Lord I thank you that I am not like the other people..." believed in divine grace). Thus we can add Augustine, Aquinas, Richard Baxter, and the New Perspective on Paul to this list (and exclude Presbyterians who don't believe covenant children are saved) and see that only the Reformed get justification correct and avoid works-righteousness, precisely and accurately following Paul.
In thinking through this, I suppose I could see a sort of 4-point Calvinism similar to Arminianism where it argues God can remove grace from you so as to cut you off from justification, where justification is still understood as resting on Christ's imputed righteousness alone and not in faith itself, which is only an instrument, nor even understanding faith as a condition for imputation (thus preserving the active/passive justification distinction). This position is basically what would happen in reality under 5-point Calvinism if Christ did not intercede for us and cause us to persevere in faith. This is the only other position I could see as not necessarily compromising justification apart from works, but I would want to think about this more.
Edit: The argument against such a "4-point Calvinism" would be that imputation gives you the right to the prize, and the prize is life eternal, so not receiving eternal life would be unjust of God due to His condescension and promise in the Covenant of Grace, so we can make that argument against it, however, the question posed above concerns whether such a position would necessarily amount to "works-righteousness", not whether it falls into other insurmountable theological errors; but I find this question impossible to answer because a situation in which one receives the imputed righteousness of Christ, yet not the benefits of that imputation is impossible to conceive of for the aforementioned reason. I therefore conclude that 5-point Calvinism is the only possible soteriology that does not logically fall prey to works-righteousness. The active-passive justification distinction is crucial here.