We want it understood that we do not reject the Law as our opponents claim. On the contrary, we uphold the Law. We say the Law is good if it is used for the purposes for which it was designed, to check civil transgression, and to magnify spiritual transgressions. The Law is also a light like the Gospel. But instead of revealing the grace of God, righteousness, and life, the Law brings sin, death, and the wrath of God to light. This is the business of the Law, and here the business of the Law ends, and should go no further.
The business of the Gospel, on the other hand, is to quicken, to comfort, to raise the fallen. The Gospel carries the news that God for Christ's sake is merciful to the most unworthy sinners, if they will only believe that Christ by His death has delivered them from sin and everlasting death unto grace, forgiveness, and everlasting life. By keeping in mind the difference between the Law and the Gospel we let each perform its special task. Of this difference between the Law and the Gospel nothing can be discovered in the writings of the monks or scholastics, nor for that matter in the writings of the ancient fathers. Augustine understood the difference somewhat. Jerome and others knew nothing of it. The silence in the Church concerning the difference between the Law and the Gospel has resulted in untold harm. Unless a sharp distinction is maintained between the purpose and function of the Law and the Gospel, the Christian doctrine cannot be kept free from error.
Martin Luther, Commentary on the Epistle to the Galatians (Kindle Locations 1659-1669). Kindle Edition.