"To justify therefore, is nothing else than to acquit from the charge of guilt, as if innocence were proved. Hence, when God justifies us through the intercession of Christ, he does not acquit us on a proof of our own innocence, but by an imputation of righteousness, so that though not righteous in ourselves, we are deemed righteous in Christ. Thus it is said, in Paul's discourse in the Acts, "Through this man is preached unto you the forgiveness of sins; and by him all that believe are justified from all things from which ye could not be justified by the law of Moses," (Acts 13:38, 39.) You see that after remission of sins justification is set down by way of explanation; you see plainly that it is used for acquittal; you see how it cannot be obtained by the works of the law; you see that it is entirely through the interposition of Christ; you see that it is obtained by faith; you see, in fine, that satisfaction intervenes, since it is said that we are justified from our sins by Christ. Thus when the publican is said to have gone down to his house "justified," (Luke 18:14) it cannot be held that he obtained this justification by any merit of works. All that is said is, that after obtaining the pardon of sins he was regarded in the sight of God as righteous. He was justified, therefore, not by any approval of works, but by gratuitous acquittal on the part of God. Hence Ambrose elegantly terms confession of sins "legal justification," (Ambrose on Psalm 118 Serm. 10)."
John Calvin. Institutes of Religion. 3.11.3