Iustitia aliena is a Latin phrase meaning “alien righteousness.” This was and continues to be the heartbeat of the Reformation– the basis of the Christian’s justification before God. The reason that we are, as Luther said, simul justus et peccator (righteous and simultaneously sinner) before God is because of this iustitia aliena credited to the Christian’s account by grace alone through faith alone in Christ alone. Without the active obedience of Christ imputed to us, God would not be both “just and the justifier of the one who has faith in Jesus” (Rom. 3:26). Thus, God declares the sinner who has faith in Christ righteous, not based on the sinner’s own righteousness, but based solely on the righteousness of Christ.
This righteousness is called alien, because it is extra nos (outside of us) and not owing to anything in ourselves. It is the basis of the theology of the cross and opposed to the theology of glory. The former bids the hopeless sinner to look outside of himself, by faith, to the cross, to the righteousness of Christ, while the latter keeps the dead sinner looking at himself and his own supposed ability to keep the law for his justification before God. Though the theology of glory flatters man that he can justify himself before God it ultimately leads to condemnation.
For as many as are of the works of the Law are under a curse; for it is written, “Cursed is everyone who does not abide by all things written in the book of the law to, to perform them.” (Gal. 3:10)
Soli Deo Gloria!