In wrapping up this series, I'm not so much responding to Sam Waldron as I am simply trying to clarify the issues. I think it is important to note that the phrase "future justification" is used by a variety of theologians but not in the same sense. Some formulations of "future justification" are more orthodox than others. I would distinguish at least three varieties (though there are probably more, I'm just not aware of them):
(1) The view of N. T. Wright and other New Perspective scholars
On this view, "future justification" is acceptance before God in the full judicial and eschatological sense of the word. This future justification will not be by faith alone but by faith and by works, that is, a person's judicial acceptance before God at the day of judgment will be determined on the basis of their obedience to the moral law. Present justification is by faith, which merely means that belief in Jesus is the badge of membership in the people of God. But future justification is on the basis of works. As N. T. Wright puts it:
And in Romans, as elsewhere in Paul, it is present justification, not future, that is closely correlated with faith. Future justification, acquittal at the last great Assize, always takes place on the basis of the totality of the life lived (e.g. Romans 14.11f.; 2 Corinthians 5.10).
[The Law in Romans 2, in Paul and the Mosaic Law (ed. James D. G. Dunn; Grand Rapids: Eerdmans, 2001), 144.]
(2) Richard Gaffin's view (as I understand it)
Gaffin takes as his starting point the doctrine of mystical union with Christ together with the already/not-yet dynamic of NT eschatology. All of the benefits of union with Christ are equally important, and none has priority, whether logical or temporal, over the others. The benefits of union with Christ can be classified into two primary groups: forensic benefits like justification and adoption, and transformative benefits like regeneration and sanctification. Both the transformative and the forensic benefits have an "already" and a "non-yet" dimension. For example, the "already" aspect of adoption is that we are now members of God's family and experience his Fatherly love and status as sons. The "not-yet" aspect is the glorification of our body. As Paul himself says, we "who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies" (Rom 8:23 ESV).
Now if adoption is both "already" and "not-yet," Gaffin reasons, and if all of the benefits of salvation are enjoyed in union with Christ, then it stands to reason that justification would also have both dimensions. We are used to thinking about the "already" aspect of justification (a past forensic declaration that we are righteous in God's sight only for the righteousness of Christ imputed to us and received by faith alone), but we should also be aware of the "not-yet" aspect of justification. The "not-yet" aspect of justification is not that we are going to be more justified or judicially accepted by God than we are now by faith, but that we will be openly acquitted and vindicated insofar as the transformative benefits of union with Christ will have worked themselves out in our lives as the effectuation of the totality of our salvation in union with Christ. On Gaffin's view, "future justification" is part of justification in union with Christ.
(3) Future vindication of one's faith by its fruits, use of "justification" only in evidentiary sense
This view is different from Gaffin's view in that it applies the term "justification" to future vindication at the day of judgment only in a linguistic rather than a theological sense. Words can be used to refer to a lot of different things because sense and reference, the two aspects of lexical meaning, are distinct. For example, the word "called" in the NT is used with at least two distinct references. When Jesus says, "Many are called, but few are chosen" (Matt 22:14), he is referring to the external, resistible call (or free offer) of the gospel. When Paul says, "Those whom he predestined he also called" (Rom 8:30), he is referring to the internal, effectual, irresistible call that is applied only to the elect. The word "call" in these two verses may have the same sense but widely different, indeed contradictory, referents. That is why we need systematic theology in addition to exegetical and biblical theology, to sort out and clarify distinctions like this.
As applied to "justification," Sam Waldron makes the following distinction,which is pretty much the same as my distinction between sense and reference:
First, when I say that the connotation of the verb, justify, here in Matthew 12:37 is an entirely different connotation than it has in Romans 3 and 4, I have in my mind the important distinction between "connotation" and "denotation." What a word connotes and what it denotes or two different things.
So Waldron is applying the term "justification" to the future vindication of the genuineness of the believer's faith by the fruit of that faith at the day of judgment only because there are a handful of verses in the NT that use the term in this way -- not to muddy the waters of the systematic locus of justification. Matt 12:37 is the only indisputed instance. James 2:21-25 may also be a case, but the focus is on the vindication of a believer's profession of faith in this life; the future aspect is not clear, although I am willing to concede that the eschatological aspect at the day of judgment may be implicit. Then there is Rom 2:13 which I do not regard as a relevant proof text (since it is part of a larger argument leading to the "empty set" conclusion of Rom 3:10-20), but which Sam Waldron does regard as relevant. That is a minor difference; on the larger point, we agree that the term "justification" is used at least once and perhaps as many as four times in the NT in reference the public vindication of one's profession of faith, a future vindication that is NOT "justification" in the technical ordo salutis sense (the imputation of the righteousness of Christ by faith alone), nor is it the "not-yet" aspect thereof (contra Gaffin). The "not-yet" aspect of justification (if we must speak of such a thing) is bodily glorification, not the vindication of the profession of one's faith on the basis of the fruit of faith, i.e., evangelical obedience.
I disagree with both (1) and (2) and, with Sam Waldron, hold to (3) -- except that I don't take Rom 2:6-13 as one of the proof texts for it as he does.