I have avoided getting into this debate because it becomes unnecessarily heated. However, I have been asked quite a few times about the issue since I made the announcement that I had come to the conclusion that UOJ is a valid Biblical concept. This is, in brief, my perspective on the issue:
There are certain terms that are used in Scripture multiple ways. Sanctification for example can be used to refer to a past event in Christ, or an ongoing action performed by the Spirit. A failure to acknowledge this had caused this whole recent sanctification controversy. The word Law is used at times to refer to the Old Testament, other times it is used to refer to commands.
Justification is the same. Most of the time, the term refers to what the sinner receives through faith alone, but other times it can refer to a past event (the resurrection) or a future event (eschatological vindication). N.T. Wright has often spoken about this; justification is a past, present, and future reality. For all of my disagreements with Bishop Wright, I think he is right on this point.
Christ's resurrection is his vindication by God. This is described in 1 Timothy 3:16,
"He was manifested in the flesh,
vindicated by the Spirit,
seen by angels,
proclaimed among the nations,
believed on in the world,
taken up in glory."
The term for vindicated in 1 Timothy is "edikaiothe", one of the words in the "dik" word group, having to do with righteousness.It is the vindication of who he is, of his sinless life, victory on the cross, and accomplishment of salvation. Through humanity's solidarity with Christ, humanity itself is vindicated. I would place this in Irenaeus' framework of the Adam/Christ parallel, wherein Christ serves not only as a representative of the new humanity, but the solitary person in which the new humanity begins and realizes itself. Thus, by participation in humanity, all in a sense participate in what Christ did to humanity through his life, death, and resurrection.
Reformed scholar Richard B. Gaffin has done some work on this, connecting Christ's vindication in 1 Timothy 3:16 and Romans 5. Paul speaks of Christ's resurrection as our justification (Rom 4:25). Through humanity's solidarity with Christ, his vindication becomes the vindication of humanity, or the justification of humanity. Gaffin of course connects this only to the elect, believing in limited atonement. Since I don't agree with that, but think his exegesis is spot on regarding this, this would mean that all of humanity has been justified through Christ's resurrection.
I would then point to Romans 5:18, "Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men." The most obvious way to read this text is to take the Adam/Christ parallel at face value. Adam brought sin and death to all. Christ, encompassing all of humanity in himself, brought justification (vindication) and life to all men. I take this "one act of righteousness" to be his resurrection which is identified with justification in 4:25.
I think theologians are right to recognize that Paul utilizes the term justification in at least two different senses. It can refer to what happened to all men in Christ at the resurrection (objective justification) and what happens to those who have faith (subjective justification). And as I pointed out previously, it can also refer to one's eschatological vindication, though that isn't part of this particular dispute.
Personally, I don't see this as a Confessional issue. I think Lutherans can have genuine disagreement here so long as both sides agree that Christ's death and resurrection were done on behalf of all people, and that the benefits of Christ's work must be received by faith. People are too quick to throw condemnations around in this debate, which is why I have largely avoided it. But, that being said, I do think that the concept of UOJ is valid and helpful. It is especially useful in explaining the Lutheran approach to universal atonement in opposition to both the Reformed and Arminian views.