Firstly, I must say that I have benefited immensely from the conversations on the doctrine of union with Christ that have ensued over the Net in the course of the past few weeks (which actually has spanned many years already). I am grateful for the contributions of great Reformed minds on both fronts, especially those whom I have had closer contact with, such as Dr. R. Scott Clark, Jared Oliphint and, just recently, Ptr. Rob Edwards (the latter two from WTS, the former from WSC).
As Ptr. Edwards noted on a comment on a blog post of mine, my use of the terms "unionism" or "unionist" may not be quite the best denomination of the view that does not see the priority of justification in the ordo salutis, a view which he espouses. His sentiment arises from the fact that the view does not in fact consider union with Christ as the overarching doctrine upon which every other doctrine has its foundation. To this I offer my apology, as it was not my intention to imply that the aforementioned assumption was the ground of my coining of the term. I merely wanted an easy name for the view. So perhaps I may now safely use the terms without fear of incurring ire.
The comment by Ptr. Edwards on my blog was prompted by my having replied to a blog post by Dr. D. G. Hart on this issue of union with Christ in which I stated that the "unionist" may have the inclination of esteeming biblical theology over systematic theology, hence the adoption of the "unionist" view. I admit the hasty generalization of the statement. However, it does appear that the "major players" in Reformed orthodoxy did hold to the priority of justification on the issue of union with Christ, specifically mystical/existential union.
Both sides of the debate hold that there are 3 aspects to union with Christ: decretal, federal, and mystical/existential. The difference lies in fact that the "unionist" does not seem to accept the classic formulation of an ordo salutis and the priority of justification in mystical union. Calvin has been thrown around by both sides of the discussion, claiming his support for their respective views. Being in agreement with the "justificationists" (there, a nickname of our own), I now seek to throw some of Francis Turretin in the mix in an attempt to show that while our every benefit in Christ does indeed emanate from our decretal and federal union with Him, the application of these benefits subjectively in mystical/existential union is through the instrumentality of faith in justification, hence its priority.
On mystical union, Turretin writes:
"Further, as long as Christ is outside of us and we are out of Christ, we can receive no fruit from another's righteousness. God willed to unite us to Christ by a twofold bond—one natural, the other mystical—in virtue of which both our evils might be transferred to Christ and the blessings of Christ pass over to us and become ours. The former is the communion of nature by the incarnation. By this, Christ, having assumed our flesh, became our brother and true Goel and could receive our sins upon himself and have the right to redeem us. The latter is the communion of grace by mediation. By this, having been made by God a surety for us and given to us for a head, he can communicate to us his righteousness and all his benefits. Hence it happens that as he was made of God sin for us by the imputation of our sins, so in turn we are made the righteousness of God in him by the imputation of his obedience (2 Cor. 5:21)" (Institutes, Vol. 2, 16.3.5).
Here we find the raising to the foreground of the foundational truth that all that we are and have in Christ is precisely ours in Christ, i.e., by virtue of our federal union with Him, we are recipients of His benefits. Notice the usage of "surety" and "head," especially the latter, which denotes the federal headship of Christ and, in the context, speaks of federal union, which further language of "communion of grace by mediation" and "communicate to us his righteousness and all his benefits" imply a future application through means.
The double evil referred to prior points to mankind as sinful universally and man in his sin as sinning particularly, which further reinforces the idea of mystical union as occurring in the subjective realm existentially.
But how is this righteousness (viz. benefits of Christ) made to be ours existentially?
The righteousness of Christ is ours through its imputation. But what is the nature of this imputation?
"For the foundation of imputation is either in the merit and dignity of the person, to whom a thing is imputed; or it is out of it in the grace and mercy alone of the one imputing. The first is the legal mode,the other is the evangelical. Hence we gather that this word is forensic. It is not to be understood physically of an infusion of righteousness, but judicially and relatively, of gratuitous acceptance in the judgment of God" (ibid., 16.3.7).
Here we find that the nature of the imputation of the righteousness of Christ is forensic, judicial, legal—the language of justification.
"Thus the imputation of righteousness is the foundation and meritorious cause of justification" (ibid., 16.4.5).
So if the imputation of the righteousness of Christ, with all its attendant benefits, is of a legal nature, and if it is the ground or cause by which we are justified, then it becomes apparent that the reception of all that we have in Christ is very closely linked to justification.
But lest we forget:
"From union with Christ depends the communion of all his benefits, of justification and of sanctification and of glory...Hence it is that, being united to Christ as our head and the first-begotten of God, his most perfect righteousness becomes ours by the imputation of God and the reception of faith, upon which depend both absolution from sins and the adoption or acceptation to life and the inheritance which is the right of sons" (ibid., 16.6.8).
Again, we find headship language in the context of union with Christ, consistent with federal union, as the dependency of our receiving of the benefits of Christ. But here we find mention of the means of reception in the existential realm, i.e. faith.
Turretin, speaking of the orthodox view on the relationship of faith to justification, declares:
"They teach that faith is the organic and instrumental cause of our justification and that justification is ascribed to it, not properly and by itself (inasmuch as it is a work or as if it was the righteousness itself by which we are justified before God; or as if by its own worth or by the indulgence of God it deserves justification in whole or in part), but improperly and metonymically (inasmuch as Christ's righteousness, which faith apprehends, is the foundation and meritorious cause on account of which we are justified). So that it is said to justify relatively and organically; relatively because the object of faith is our true righteousness before God; organically because faith is the instrument for receiving on our part and for applying to ourselves, that righteousness" (ibid., 16.7.5).
So the language of "justified by faith" is a metonymy of justified by the imputation of the righteousness of Christ; and, if as the preceding treatments indicate, the benefits of Christ are ours through imputation, then it follows that these benefits are ours by faith.
So if the imputation of the righteousness of Christ is faith, metonymically, and the former is of a forensic nature, then it must indeed follow that our reception of the righteousness of Christ, in mystical/existential union, is predicated on justification by faith.
On the causal nature of justification, Turretin adds (referring to sanctification as "regeneration"):
"Paul does not say that we are justified by regeneration (Tit. 3:5-7); nay, since he ascribes justification to the grace of God and takes away from works, he shows that he is unwilling to ascribe it to righteousness inhering by regeneration, which is rather the fruit than the cause of justification. But his intention is to point out how God will have us saved by two benefits which he bestows upon us—regeneration, of which the Holy Spirit is the author in us; and justification, which we obtain by Christ, by which we are made heirs of eternal life. That denotes the way of salvation [referring to sanctification - mine], this its cause [referring to justification - mine]" (ibid., 16.2.21, emphasis mine).
Given the data above, it does seem to appear that Francis Turretin himself was a "justificationist." While holding to the priority of union with Christ as the source of all our benefits in Him, the holding is a qualified one.
Universally, the Christian's ground of participating in the benefits of Christ is both decretal (election) and federal union (historia salutis); particularly, the ground is mystical/existential union predicated upon justification by faith.
Covenantally, it does make sense. How can the covenant-breaker (Covenant of Works) be made to be a partaker of the privileges of being in the Covenant of Grace without first having been declared in good-standing with the Covenant Lord through a forensic, legal pardon that is appropriated through justification by faith? If justification does not precede mystical union, then it follows that one under the Covenant of Works can indeed enjoy the benefits of the Covenant of Grace—a problematic proposition.