*this is my 10th post in the current series on the NPP
Why do we need the imputed righteousness of Christ? Simply put: we are dead in sin (as an aside, I feel the NPP softens the harshness of God’s wrath towards sin and the problem God’s wrath presents for man). We can do nothing to help ourselves and must be rescued. We cannot accomplish anything toward our own salvation. We must rely entirely on an outsider to save us (Romans 3:23). Paul writes in Romans 3:20, “For by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin.” We have no means at our disposal to earn our justification. As R.C. Sproul writes, “In a synthesis, something new is added to something basic. Our justification is a synthesis because we have the righteousness of Christ added to us. Our justification is by imputation. God transfers to us, by faith, the righteousness of Christ, to whom we now belong. It is a real imputation.”
On this last point of a real imputation, hear another non-imputation advocate from another era in Vincent Taylor, who says imputation is, “an ethical fiction” because righteousness cannot imputed to a sinner any more “than bravery to a coward or wisdom to a fool”. Taylor goes on to say if a man is counted as righteous, it must be because “he is righteous, and not because another is righteous in his stead.” This objection can be found in almost all NPP writings in some form or another.
For example, Wright’s famous slam on imputation runs as follows: “It makes no sense whatever to say that the judge imputes, imparts, bequeaths, conveys or otherwise transfers his righteousness to either the plaintiff or the defendant. Righteousness is not an object, a substance or gas which can be passed across the courtroom.” E.A. Knox, wrote beautifully on this nearly a century prior: “Why should he not speak of an imputed righteousness, or of Christ’s righteousness reckoned to him? If Christ lives in him, what should God see in him, of what should God take account in him, but of the living indwelling Christ in all His perfect righteousness?” 
Millard Erickson is helpful here when he explains imputation is not an external, arm’s length, two-party matter: “When looking at the believer God the Father does not see him or her alone.” Instead, “it is as if God says, ‘They are righteous’!” But how does God constitute “the believer one with Christ”? Erickson explains the "situation is somewhat analogous to what takes place when two people marry or two corporations merge: their separate assets are brought into the union and are thereafter treated as mutual possessions.” Is not this portrait of our union with Christ warmer, more intimate, more spectacular and ultimately, more biblical than the NPP version? When an NPP advocate calls the whole idea of imputation a fiction, they are not seeing our union with Christ in its full radiance (Romans 6:1-11). In my opinion, not only is imputation more theologically sound than the NPP on justification, it is also more awe-inspiring and praise worthy.
 Cf. Ephesians 2:12-13 and Romans 1:1:18-3:20.
 R.C. Sproul, Essential Truths of the Christian Faith (Wheaton, IL: Tyndale, 1992), 190. See the helpful diagram on this in Appendix A.
 Vincent Taylor, Forgiveness and Reconciliation (London: Macmillan, 1952), 57. Taylor is an older source and not mentioned often in the current debates. I found the wording of his objection helpful because the explicit way he denies imputation was so clear and telling.
 Wright, Saint Paul, 98. Douglas Wilson has a humorous and effective response to Wright’s category error here: http://www.dougwils.com/N.T.-Wrights-and-Wrongs/A-Category-Mistake.html . Wilson has his own set of mistakes by holding to Federal Vision theology but this does not disqualify him from funny and accurate responses to NT Wright on justification!
 Edmund Arbuthnott Knox, The Glad Tidings of Reconciliation (London: Longmans, 1916), 74.
 Millard J. Erickson, Christian Theology, Second Ed. (Grand Rapids, MI: Baker, 2003), 971-972.
 For more insight on this from the Reformers, see especially John Calvin, Institutes 3.11.5 and to a lesser (but still valid) extent, Martin Luther in Luther’s Works, ed. Helmut T. Lehmann (Philadelphia: Fortress, 1971), 31:298. In these places they speak of the relationship between imputation and union with Christ. They do this in contrast to later, more theologically liberal authors who create a false dichotomy between imputation and union. For more on union with Christ, see Chapter 18 “Union with Christ” in Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims on the Way (Grand Rapids, MI: Zondervan, 2011).
 NPP writers often say we can get everything we need from union with Christ without recourse to imputation. I disagree. Besides, if the concept of reckoning or counting us righteous in Christ is indeed a biblical one - and I believe it certainly is - then we should not jettison it from our theology so easily.