In part of course this depends on who we are talking to, or writing for, and how well the terms being used are understood. Gone are the days of theological literacy among evangelicals where terms like "imputation," "justification" and "active obedience" were well understood. Granted, at some point we all had to learn them, and we shouldn't feel bad, or be made to feel bad, about our ignorance of the meaning of specific terms. My point is not about whether we were taught them as children or adults, but that these words were clearly inscribed on the coinage of the evangelical realm. Evangelicalism has, however, worn down these definitions and has either not bothered to mint new ones with the same inscription (through neglect) or accepted alternative currencies. To change the image, there has been a deforrestation of well understood and well used theological words for some time among evangelicals.
Along with this has come a failure to distinguish not only what was at stake in major historic debates but even what the debates themselves were really about. What were the Reformers reacting against? Well, we might say it was justification by works. The Reformers taught that justification was by grace and the Medieval Roman Catholic church taught that it was by works. If we think those were the terms of the debate we would be wrong. Rome did not exclude grace from salvation, or justification. In fact for Rome grace preceded works.
Being muddled about historic debates may not ordinarily be a costly thing, but in theology it can be. Instead of seeing three distinct, and mutually exclusive, positions on grace and works we could end up thinking that there are only two. The three can be summed up with the following anthems and explanations:
1. "We can do it, yes we can!" Pelagianism. Justification by works. If we are to be right with God then we will do it by raw, unassisted, obedience to law. Keep God's commands and you will be righteous in his sight and have eternal life.
2. "God helps those who help themselves." Semi-Pelagianism. Justification by works assisted by grace. If we are to be right with God then this cannot happen apart from God's grace. Grace is essential to salvation, and grace works in us (and we work by grace) in order that we might be justified. God will not withold his grace to those who do what lies within them.
3. "My friend will pay." Reformation theology. Justification by faith alone, by grace alone, through Christ alone. We are not justified on the basis of our works, assisted by God or done out of raw human effort. We are justified through faith on account of the work of Christ, by his obedience and satisfaction. This is counted as ours and received by faith resting and relying on Christ.
If we imagine that the Reformation was about the conflict between views 1) and 3) we will certainly think that the Reformation is over and that there is no barrier to Christian unity today as evangelicals and the Roman Catholic church both teach that we are right with God because of his grace. Added this is the temptation to conflate the covenants so that there is no difference between their principles (grace and works, law and promise, "do this and live" and "it is finished"). What you then end up with is a distinction between initial and final justifcation that looks like 2) and is not represented by 3).
All of this is relevant for the current controversies about justification. Mike Horton has done a stellar job on this in his latest book Covenant and Salvation: Union with Christ. Here are some more extracts:
On the New Perspectives, covenantal nomism, and the Reformation:
The attempt to exonerate Judaism from works-righteousness does not succeed, from a Reformation perspective, simply by showing that it is not Pelagian, since medieval theology was clearly not Pelagian either. (p. 40)
The position that Sanders has thus far described is remarkably similar to the position of the late medieval nominalism in which Luther was schooled and which he strenously rejected...According to this theology, no one deserves salvation in any strict sense, but God has decreed a covenant according to which those who do their best (assisted by grace) will attain final justification as if they had merited it.
Indeed "getting in by grace and staying in by obedience" admirably summarizes the covenantal nomism of the medieval system as it evolved especially in nominalism and become officially sanctioned at Trent. Baptism, the first justification, was by grace alone (an infusion of grace that wiped away original sin and filled the passive recipient with a transformed habitus), followed by various sacramental resources for co-operating grace, which (hopefully) would lead to final justification in the life to come.
Paul F.M. Zahl's comment is exactly right: "E.P. Sanders mistakes the 'semi-Pelagianism' of Second Temple Judaism for 'Pelagianism' and thus misunderstands Luther's critique of the Roman Catholic Church as well as Luther's grasp of Paul." (p. 41-2).
There is no "view from nowhere," even for biblical scholars, and the vista from which the NPP assays the horizon of Paul and Palestinian Judaism is well defined as covenantal nomism. It is a synergistic perspective that, for all of the important differences, unites Judaism, the medieval theology codified at Trent, and includes myriad Protestant attempts in the modern era all the way to the present moment. (p. 49).