There is no gospel without the truth of justification by faith. Some have problems getting their hands around this subject. Many do not fully understand what the doctrine is all about. Justification (dikaioo) carries the idea of being completely acquitted of sin before the bar of God. The Lord imputes (puts to our account) the very righteousness of Christ. Therefore God sees us clothed in His righteousness not our own. Paul saw the things he had accomplished as dung "in order that (as he said) I may gain Christ, and may be found in Him, not having a righteousness of my own derived from the Law" (Phil. 3:8b-9). Salvation he adds, "is through faith in Christ, the righteousness which comes from God on the basis of faith" (v. 9b).
The words justification and righteousness are really one word. "Justification" is generally the word as a verb; "righteousness" is the noun. We do not earn this justification, it is imputed, imparted to us as a free gift based on our trust in Christ.
The Roman Catholics teach that by faith one starts the justification process or that it is but the first stage towards salvation. A person then must complete justification by works, by self efforts. But the Scriptures teach that it is a completed work in that only God could accomplish such acquittal because of the work of Christ on the cross.
To be legally acquitted, or justified, is an Old Testament concept. The key verse has to do with Abraham in Genesis 15:6. Abraham believed what God had promised and God in turn then saw him as one legally acquitted in His sight. "Abraham believed God and He counted it to him for righteousness." Even Abraham and all the Old Testament saints would be justified only by the forward coming work of Christ on their behalf on the cross. In prophecy Isaiah 53:11-12 says, "My Servant (the coming Messiah) will justify the many, as He will bear their iniquities. … Yet He Himself will bear the sin of many, and intercede for the transgressors."
Christ illustrated this justification in His story about the Pharisee and the Tax Collector in Luke 18:10-14. The self-righteous Pharisee thought he deserved the favor of God by his good deeds but then reasoned that the Lord would look down with disfavor on the Tax Collector. But it was the Tax Collector who confessed his sins. Christ said the Tax Collector "went down to his house justified rather than the (Pharisee)." When the Tax Collector cried out "God, be merciful to me, the sinner!" he was claiming the grace of God as exemplified in the Mercy Seat in the temple.
In my Luke Commentary I write,
"Paul says that God ‘justified as a gift by His grace through the redemption which is in Christ Jesus’ (Rom. 3:24). Now in the church age, this happens by direct trust in Jesus, the object of faith, because of His finished work at the cross. Paul says that we receive ‘the righteousness of God through faith in Jesus Christ [meant] for all those who believe’ (Rom. 3:22)." (p. 178)
It may be said that justification is the cornerstone of salvation and the gospel. This is certainly indeed "good news." God through His Son has done it all for lost sinners.
This justification is complete and whole. We are seen as righteous as the Son of God by the fact that this righteousness has been put to our account. Whom God saves and justifies cannot be "un-justified". As with the Pharisee in the Luke 18 story, we have a choice to "be trusting in ourselves" or trusting in the finished work of Christ! Trusting Him gives eternal life and this truly is good news—the gospel!