Take Romans for instance. In Romans 4:1-8, faith is "credited" or "counted" as righteousness. At the end of Romans 4 in verse 25, all of a sudden we read that Christ "was raised for our righteousness". So faith is counted as righteousness because of Christ's resurrection.
Then into chapter 5:1, we have righteousness "by/through faith" which is also "through Jesus Christ". Then in verse 9, we are "righteous-ed by his blood". In 5:18, 19 we read that it is the obedience of the one man (I think this fits better than "one act of obedience") that makes many righteous. It is tempting to read Romans 4:1-8 and offer the reductionist argument that since faith is credited as righteousness, any kind of place for Christ's righteousness must be excluded. But this argument fails to deal with the complicated nuances each text brings to the complete view.
Furthermore, if we hark back to Romans 3 and assume that the subjective reading of pistis Christou is correct (a grand assumption I realise), the picture is filled out even futher. We read in verse 22 that the righteousness of God is given "through the faithfulness of Jesus Christ to all who have faith." (The idea of the faithfulness of Christ would create a remarkable contrast with unfaithful Israel in verse 3).
So to chronologically sum up:
- God reckons faith as righteousness apart from works.
- God reckons us righteous and gives us peace through Christ.
- God reckons us righteous on account of Christ's resurrection.
- God reckons us righteous on account of Christ's blood.
- God reckons us righteous on account of Christ's obedience in place of the disobedient first Adam.
- God gifts righteousness through Christ's faithfulness, because there are none who are faithful, no not one.