Galatians 2:21

I do not make void the grace of God: for if righteousness is through the law, then Christ died for naught.

The great problem existing from the day man first committed sin is, "How can even God justly declare a human being to be righteous?" That the Law of Moses could not do it is an axiom. If true righteousness could have been procured by any man who ever lived on earth through means of the Mosaic Law, Christ's death would not have been necessary. The corollary of that is that for one to rely upon law-keeping for justification is to repudiate and reject Christ' sacrifice.

And how does God justly account a man to be righteous? It is not by shooting righteousness into him gratuitously because he believed, but by transferring the sinner into Christ who IS righteous, the sinner first of all renouncing his own identity, in the sense of having any merit (as Jesus said, "denying himself"'), being baptized into Christ and remaining "in him" until the final summons. It is the perfect faith and righteousness of Jesus Christ which constitute "the righteousness of God through the FAITH OF CHRIST" (Romans 3:22-26). Please see my Commentary on Romans, chapter 3, for extensive discussion of this.