Charles Hodge: God, who is perfectly just, requires perfect righteousness in those whom He accepts

"The Apostle, having taught that God is just, i.e., that He demands the satisfaction of justice, and that men are sinners and can render no such satisfaction themselves, announces that such a righteousness has been provided, and is revealed in the Gospel. It is not our own righteousness, which is of the law, but the righteousness of Christ, and, therefore, the righteousness of God, in virtue of which, and on the ground of which, God can be just and yet justify the sinner who believes in Christ. As long as the Bible stands this must stand as a simple statement of what Paul teaches as to the method of salvation. Men may dispute as to what he means, but this is surely what he says." –Charles Hodge in “Systematic Theology,” vol. 3