For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faithRomans 1:17
God is righteous. But what does that mean?
1. Just; accordant to the divine law. Applied to persons, it denotes one who is holy in heart, and observant of the divine commands in practice; as a righteous man. Applied to things, it denotes consonant to the divine will or to justice; as a righteous act. It is used chiefly in theology, and applied to God, to his testimonies and to his saints.http://webstersdictionary1828.com/Dictionary/righteous
God is Holy, and is consistent with His commands. But the amazing thing is that God is willing to impute His righteousness to us!
Martin Luther discovered that God not only reveals His righteousness by faith, but that the just can live by faith (Romans 1:17). Then Luther read about Abraham:
For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness.Romans 4:3
and then about David:
Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,Romans 4:6
God imputes – adds to our account – His righteousness! Not by works, but by faith! Let’s thank Him for the righteousness He has – but that He has given us!