The Lord says: "Lift up your eyes to the heavens, and look upon the earth beneath; for the heavens shall vanish away like smoke, and the earth shall wax old like a garment; and they that dwell therein shall die in like manner; but my salvation shall be forever and my righteousness shall not be abolished. Hearken unto me, ye that know righteousness, the people in whose heart is my law" (Isa. 51:6, 7). "My tongue shall speak of Thy work; for all Thy commandments are righteousness" (Ps. 119:172).
The righteousness of God, therefore, is His law. Let this not be forgotten. The term "the righteousness of God" occurs frequently in the book of Romans, and much confusion has resulted from giving it arbitrary and varying definitions. If we accept the definition given in the Bible, and do not abandon it in any instance, it will simplify matters very much. The righteousness of God is His perfect law.
But the Ten Commandments, whether engraved on tables of stone or written in a book, are only statements of the righteousness of God. Righteousness means right doing. It is active. The righteousness of God is God's right doing, His way. And since all His ways are right, it follows that the righteousness of God is nothing less than the life of God. The written law is not action, but only a description of the action. It is a picture of the character of God.
The very life and character of God are seen in Jesus Christ, in whose heart was the law of God. There can be no righteousness without action. And as there is none good but God, it follows that there is no righteousness except in the life of God. Righteousness and the life of God are one and the same thing.
"For therein is the righteousness of God revealed." Wherein? In the gospel. Bear in mind that the righteousness of God is His perfect law, a statement of which is found in the Ten Commandments. There is no such thing as a conflict between the law and the gospel. Indeed there are not in reality two such things as the law and the gospel. The true law of God is the gospel; for the law is the life of God, and we are "saved by His life." The gospel reveals the righteous law of God, because the gospel has the law in itself. There can be no gospel without law. Whoever ignores or rejects the law of God, has no knowledge whatever of the gospel.
"Waggoner on Romans" : Ellet J. Waggoner : p. 1.24, 25