From Martin Luther’s Introduction to the Commentary on Paul’s Epistle to the Galatians:
I have taken in hand, in the name of the Lord, once again to expound the Epistle of St. Paul to the Galatians; not because I desire to teach new things, or such as you have not heard before, but because we have to fear, as the greatest and nearest danger, that Satan take from us the pure doctrine of faith and bring into the Church again the doctrine of works and men’s traditions.
The devil, our adversary, who continually seeks to devour us, is not dead; likewise our flesh and old man is yet alive. Besides this, all kinds of temptations vex and oppress us on every side. So this doctrine can never be taught, urged, and repeated enough. If this doctrine is lost, then is also the whole knowledge of the truth, life and salvation lost. If this doctrine flourishes, then all good things flourish.
Are we in danger of losing the Gospel, or have we lost it already?