Let the Law have its glory. But no Law, no matter how divine or holy, has the right to tell me that I obtain justification and life through it. I will grant that it can teach me that I should love God and my neighbor, and live in chastity, patience, etc.; but it is in no position to show me how to be delivered from sin, the devil, death, and hell. For this I must consult the Gospel and listen to the Gospel, which does not teach me what I should do—for that is the proper function of the Law—but what someone else has done for me, namely, that Jesus Christ, the Son of God, has suffered and died to deliver me from sin and death. The Gospel commands me to accept and believe this, and this is what is called “the truth of the Gospel.” It is also the main doctrine of Christianity, in which the knowledge of all godliness is comprehended. It is, therefore, extremely necessary that we come to know this doctrine well and constantly inculcate it. For it is delicate and is easily bruised, as Paul had learned and as all the saints have often experienced.
--Martin Luther, LW26, Lectures on Galatians