For not that which I (new nature) desirously will, to do good, but that bad which I (new nature) do not desirously will, this I (old nature) practice, (Romans 7:19).
If righteousness could come through law, then living by the law should result in freedom from the strong cravings of the flesh. However, law simply does not produce the desired effect. Through law, we seek to live out righteousness, yet instead of gaining freedom from the cravings of the flesh, the old nature works out its practices in opposition to what we desire to do.