Justification is a legal act whereby God declares the sinner to be innocent of his or her own sins. It is not that the sinner is now sinless, but that he/she is declared sinless. This declaration of righteousness means the person is justified before God. This justification is based on the shed blood of Jesus, having now been justified by his blood.

Rom 5:9;

Since we have now been justified by his blood, how much more shall we be saved from God’s wrath through him!

Where Jesus was crucified, died, buried and rose again.

1 Cor 15:1-4;

Now, brothers and sisters, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand.² By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain.

³ For what I received I passed on to you as of first importance^[a]: that Christ died for our sins according to the Scriptures,⁴ that he was buried, that he was raised on the third day according to the Scriptures.

God imputed (reckoned to our account) the righteousness of Christ at the same time our sins were imputed to Christ when he was on the cross. That is why it says in

1 peter 2:24;

 “He himself bore our sins” in his body on the cross, so that we might die to sins and live for righteousness; “by his wounds you have been healed.”

And He Himself bore our sins in His body on the cross that we might die to sin and live to righteousness; for by His wounds you were healed.

Also 2 Cor 5:21;

God made him who had no sin to be sin^[a] for us, so that in him we might become the righteousness of God.

Says, He made Him who knew no sin to be sin on our behalf that we might become the righteousness of God in Him. Additionally, we are justified by faith

Rom 5:1;

Therefore, since we have been justified through faith, we^[a] have peace with God through our Lord Jesus Christ

Apart from works of the law

Rom 3:28;

 For we maintain that a person is justified by faith apart from the works of the law.