“So then as through one transgression there resulted condemnation to all men, even so through one act of righteousness there resulted justification of life to all men” (Romans 5:18).
Federal Visionists love this verse because they think that it is appropriate to say that we are justified by the death of Christ. They argue that “one act of righteousness” must be referring to the cross, not the law-keeping of Christ. Therefore, we are justified by the death of Christ. Obviously, this is a denial of the imputation of the active obedience of Christ.
The Reformed faith has always insisted that justification consists of two parts. First, we receive the forgiveness through the death of Christ. Second, we receive life through the transfer of the righteousness of Christ to us.
For justification to be Justification, you need both parts of Christ: his life and death. Forgiveness of sins is no good unless we also receive his righteousness. Thus, to say that we are justified by one act of righteousness is incomplete, at best. Rather, we are justified by many acts of righteousness.