A few thoughts inspired by dialogue with the New Perspective on Paul.
Properly understood, it is not my faith in Jesus that saves me. Rather, it is the faithfulness of Jesus that saves me.
My faith does not defeat the power of sin, nor does it atone for my sins. Rather, it is the faithfulness of Jesus that has defeated sin and atoned for the sins of us all.
My faith does not recapitulate humanity, nor does it inaugurate the new age. Rather, it is the faithfulness of Jesus that recapitulated humanity and birthed the new age.
Therefore, it is the faith of Jesus that is salvific, not my faith in Jesus. My faith in Jesus simply shows that I have been saved by Jesus. My faith is not what gets me into the covenant people of God, it is that which shows that I am already in the covenant people of God. Faith in Jesus is not that which saves Christians, rather it is that which is an identity marker of those who have already (in the here-and-now) realized that they have been saved by Jesus. Faith simply sets apart those who have already realized that Jesus is Saviour and Lord of all, until the day when Jesus returns and God becomes “all in all.”
However, there are another dimension to Christian faith in Christ. Indeed, Christian faith is perhaps better described as in Christ faith. That is to say, it is the faith of those who are in Christ. Indeed, one of the the most central elements of Paul's writing is the notion of Christian existence “in Christ.” Christians are those who members of Christ's body, they are baptized into Christ's death so that they will be resurrected with Christ, they share in Christ's sufferings so that they may also share in his glory, therefore Christian living can be summed up as “Christ” (as Paul says in Phil 1.21: “For me, to live is Christ”). Therefore, because all that we are and do is now “in Christ” this means that our faith is “in Christ faith.” Understood in this way, it is possible to see our faith as participation in the faith of Christ.
Realizing this also opens the door to revisit the notion of type of righteousness possessed by Christians. Certain New Testament scholars have raised a significant critique of the Reformed doctrine of “imputed righteousness.” This doctrine asserts that God gives his own righteousness to believers and thus considers them innocent. However, the critics of this doctrine have argued that to suggest that believers are granted God's righteousness is to make a category mistake. What they mean is this: righteousness language in the New Testament is best understood against two backgrounds, the forensic (i.e. law court) and the covenantal. Now, in the law court there can be more than one type of righteousness. There is the righteousness of the judge, who judges impartially and justly, and there is the righteousness that is granted to the defendant when he or she is vindicated. Thus, when righteousness language refers to God as judge and to humanity as the defendant, one must not suggest that one can share in the other's righteousness for that would confuse the categories. The defendant is not declared righteous in the same way that the judge is righteous. Furthermore, the same distinction holds within the covenantal context. Here God's righteousness is understood has his faithfulness to the covenant he made, and to suggest that human's receive this righteousness is to confuse the covenant partners with one another. This critique, I think, is quite convincing.
However, there is a sense in which the notion of “imputed righteousness” still holds true, but it does so in a significantly reworked manner. Stated succinctly: because the in Christ faith of believers is participation in the faith of Christ, believers also participate in God's righteousness because they then become the agents by which God remains faithful to his covenant with humanity and the rest of creation. The notion of “imputed righteousness” is therefore all about vocation, commission, and mission, and not about some sort of static status. One can be said to share in God's righteousness to the extent that one shares in God's mission. Indeed, this is also then a participation in God's righteousness as judge over the world, and perhaps this view of imputed righteousness makes good sense of Paul's enigmatic statement that “the saints will judge the world” (cf. 1 Cor 5-6). Christian's share in God's righteousness as judge when they go into the world with the embodied announcement of the forgiveness of sins.