“I have taken in hand, in the name of the Lord, yet once again to expound this epistle of St. Paul to the Galatians; not because I desire to teach new things, or such as ye have not known before, since that, by the grace of Christ, Paul is now thoroughly known unto you, but for that we have to fear lest Satan take from us this doctrine of faith, and bring into the Church again the doctrine of works and men’s traditions.  Wherefore it is very necessary that this doctrine be kept in continual practice and public exercise, both of hearing and reading.

And although it be never so well known, yet the devil, who rageth continually, seeking to devour us, is not dead.  Likewise our flesh and old man is yet alive.  Besides this, all kinds of temptations do vex and oppress us on every side; so that this doctrine can never be taught, urged, and repeated enough.  If this doctrine be lost, then is also the doctrine of truth, life, and salvation, also lost and gone.  If this doctrine flourish, then all good things flourish; religion, the true service of God, the glory of God, the right knowledge of all things which are necessary for a Christian man to know.”

Copied from the preface of Luther’s commentary on Galatians.