More from Walther...

(from "Law and Gospel" - the 29th Evening Lecture):

Every true preacher and servant of Christ will be filled with earnest zeal, even though his only return may be unpopularity and even bitter hatred. A true preacher will prefer that to being on good terms with everybody as a result of concealing or blunting the truth.

Thus, my friends, it cannot be denied: A preacher, especially a zealous one, must take his preaching very seriously, or else he commits grave sin. But he can also sin by going beyond the Word of God in what he says about Christianity and its demands.

(from the 28th evening lecture):

When, for example, a preacher wrongly reproves, and this is heard by pious, conscientious Christians who work out their salvation with fear and trembling, it may easily happen that such dear souls now become uncertain about their state of grace and doubt whether they will be saved. Then the preacher must not think that he will straighten out everything in a later sermon. No, the more the hearers look upon their pastor as orthodox and a genuine, experienced Christian, the less will they be able to surmount the trouble when he has shot the arrow of a false rebuke into their hearts.

Or he may offer false comfort where he should have rebuked, and false Christians enjoy it and compliment themselves on being good Christians. How terrible when a carnal-minded and secure person regards himself as a good Christian, even though the opposite is the case! He will go on in his blindness and finally be eternally damned.