Paul has already explained the doctrine of justification in this letter and only needs to mention the word in order for his readers to know that he is referring to a significant doctrine. We can remind ourselves of its basic features.
First, the doctrine of justification describes how God as judge deals with a converted sinner.
Second, justification has to do with the removal of barriers that prevent us from being accepted by God. God could not accept us as long as those barriers remained because he is a righteous God who must punish those who sin against him.
Third, justification is the remedy of God alone to deal with the problem. The solution did not come from outside of him. It is an expression of his wisdom as well as of his love. His wisdom is seen because in justification he deals with the problem of forgiving a guilty sinner who deserves to be punished. The just God by his wisdom found the solution that allowed him not to punish the guilty.
Fourth, justification through the work of Christ deals with the twofold problem that each sinner has. Those problems are (1) his responsibility to provide God with a lifetime of perfect obedience and (2) his responsibility to provide the payment for all the sins he had committed against God. How did God deal with those two problems? He sent his Son to do so and by his perfect life he dealt fully with the first problem and by his death on Calvary he dealt fully with the second problem.
Fifth, sinners enter into the state of justification by faith in Jesus. When they initially believe in Jesus, God the Father imputes to them the benefits of what Jesus purchased for them through his life and death. His perfect lawkeeping is imputed to them as their standing in the presence of God and makes them accepted in the Beloved. His atoning death ensures the forgiveness of all their sins.
Sixth, justification does not make us righteous. Instead we are declared to be righteous by God in his sight. The person declared righteous by God does have a new nature through regeneration, but he is still a sinner. Yet he is also regarded as righteous as far as the penalty for sin is concerned. It is important that justification is not something done by us, nor is it based on something done in us; instead it is something done for us by the Father because the Son did something for us in his life and death.
Seventh, the status of justified cannot be altered by the sins that a believer will commit after his conversion. Nor is it confirmed or made more secure by the repentance or the dedication that the believer will have after his conversion. Justification is a judicial act of the Father based on the perfect work of his Son.