Cosmic Treason by RC Sproul

The only righteousness that meets the requirements of the Law is the righteousness of Christ. It is only by imputation of that righteousness that the sinner can ever possess the righteousness of the Law. 

This is critical for our understanding in this day where the imputation of the righteousness of Christ is so widely under attack. If we abandon the notion of the righteousness of Christ, we have no hope, because the Law is never negotiated by God. As long as the Law exists, we are exposed to its judgment unless our sin is covered by the righteousness of the Law. The only covering that we can possess of that righteousness is that which comes to us from the active obedience of Christ, who Himself fulfilled every jot and tittle of the Law. 

His fulfilling of the Law in Himself is a vicarious activity by which He achieves the reward that comes with such obedience. He does this not for Himself but for His people. It is the background of this imputed righteousness, this rescue from the condemnation of the Law, this salvation from the ravages of sin that is the backdrop for the Christian’s sanctification, in which we are to mortify that sin that remains in us, since Christ has died for our sin. 

 R. C. Sproul  Cosmic Treason