In the reformed doctrine, we elaborate how we are counted heaven-worthy.
This brings in the doctrine of Christ's active and passive obedience.
Active Obedience: The righteous works of Jesus on Earth.
Passive Obedience: The suffering Christ endured in crucifixion.
The dispensationalists consider only the passive obedience of Christ, concerning our salvation. That we are saved because Christ took our sins. Because Christ died for us. The Catholics called theirs "infused righteousness" instead of the Reformation's "imputed righteousness". Infused righteousness is the infusion of the saints' righteousness through the sacraments.
However, that is not enough, because that only makes us sinless. To truly be saved, we must not just be completely sinless, such as rocks and stones, we must also be righteous!
This is where the active obedience of Christ comes in. By this, Christ's righteousness is imputed upon us.
An important note: I was once perplexed by Christ's response in Matthew 3:15, but this is the fulfillment of the Active Obedience of Christ, His righteousness!
Matthew 3:15 ... Suffer it to be so now: for thus it becometh us to fulfil all righteousness.
Hence, the double imputation: Christ Righteousness to us. Our sins to Christ.
Sources:
R. C. Sproul
Theopedia
Monergism