It's not surprising you get this wrong. It was the core impetus for the Reformation.
In opposition to this doctrine, the Reformers maintained that by justification the Scriptures mean something different from sanctification. That the two gifts, although inseparable, are distinct, and that justification, instead of being an efficient act changing the inward character of the sinner, is a declarative act, announcing and determining his relation to the Law and justice of God. In the second place, the Symbols[3] of the Reformation no less explicitly teach that justification is not simply pardon and restoration. It includes pardon, but it also includes a declaration that the believer is just or righteous in the sight of the Law. He has a right to plead a righteousness which completely satisfies its demands. And, therefore, in the third place, affirmatively, those Symbols teach that justification is a judicial or forensic act, i .e ., an act of God as Judge proceeding according to Law, declaring that the sinner is just, i .e ., that the Law no longer condemns him, but acquits and pronounces him to be entitled to eternal life...""By this the Reformers intended, in the first place, to deny the Romish doctrine of subjective[1] justification. That is, that justification consists in an act of God making the sinner subjectively holy. Romanists confound or unite justification and sanctification. They define justification as “the remission of sin and infusion of new habits of grace.” By remission of sin they mean not simply pardon, but the removal of everything of the nature of sin from the soul. Justification, therefore, with them, is purely subjective, consisting in the destruction of sin and the infusion[2] of holiness.
And here...
I. As in the chain of salvation Justification follows Vocation, Rom. 8:30, and is everywhere set forth as the primary effect of faith. The topic concerning Vocation and Faith begets the Topic concerning Justification, which must be handled with the greater care and accuracy as this saving doctrine is of the greatest importance in religion. It is called by Luther, the article of a standing and falling church; by other Christians it is termed the characteristic and basis of Christianity not without reason, the principle rampart of the Christian religion, and, it being adulterated or subverted, it is impossible to retain purity of doctrine in other places. Whence Satan in every way has endeavored to corrupt this doctrine in all ages; as has been done especially in the Papacy: for which reason it is deservedly placed among the primary causes of our Secession from the Roman Church and of the Reformation...""Is the word Justification always used in a forensic sense in this argument, or also in a moral and physical? The former we affirm, the latter we deny, against the Romanists.
God give you ears to hear the truth. We are saved by Christ's righteousness alone.
"Justification, the cardinal principle of the Reformation, is the heart of the Reformed or Presbyterian faith as truly as it is of the evangelical or Lutheran doctrine. It refers to the divine act whereby God freely makes humans, who are sinful and therefore worthy of condemnation, acceptable before a God who is holy and righteous. Justification is forensic (that is, it is "courtroom language"). We are declared, counted or reckoned to be righteous when God imputes the righteousness of Christ (an "alien righteousness") to our account. In other words, the Judge of all the earth declares us "not guilty" when we believe because Christ was pronounced "guilty" for us on the cross. We are not first made righteous, then declared righteous; we are declared righteous by grace through faith in Christ, then made righteous! When we believe, God imputes Christ's righteousness to us 'as if' it were our own. However, it is HIS righteousness, that is why Paul says in Romans 1:17 that there is a righteousness that has been revealed from God, a righteousness not of our own, but a righteousness revealed from God and freely given to those who do not work, but to those who believe." - By Charles R. Biggs
You wrote:
"It's not surprising you get this wrong."
I didn't get this wrong.
"It was the core impetus for the Reformation."
So one error propelled another? No surprise there. Look, if the PURELY forensic way of looking at justification were the correct understanding you would think someone would have known about it BEFORE the 16th century wouldn't you?
"God give you ears to hear the truth. We are saved by Christ's righteousness alone."
We are saved by ONLY Christ's grace that He won for us on the cross. And that neither suggests a forensics only justification or necessitates a forensics only justification. Perhaps you didn't realize that?
I suggest you look here: http://ic.net/~erasmus/ERASMUS7.HTM#FAITH%20ALONE%20(%20SOLA%20FIDE)%20AND%20IMPUTED