Luther clearly understood the difficulties associated with preaching well--truthfully and with doctrinal precision. His words on John 15 are helpful both to pastor and parishioner alike and emphasize the necessity of preaching faith and good works:
"So there are two parts of Christian teaching that we must emphasize daily. Neither faith nor works can be ignored. For when faith isn't preached--when no one explains how we are joined to Christ and become branches in him--then everyone resorts to their own works. On the other hand, when we teach only about faith, this lopsidedness leads to false Christians. These people praise faith, are baptized, and even call themselves Christians, but they don't show any fruit or power.
"That's why it's so difficult to preach. No matter how I preach, something goes wrong. Someone always goes off on a tangent. If I don't preach about faith, the result will be useless and hypocritical works. If I only emphasize faith, no one does any good works. The result is either useless, faithless do-gooders or believers who don't do any good works. So we must preach the message to those who accept both faith and works. We must preach to those who want to remain in the vine, put their trust in Christ, and put their faith into action in their everyday lives."
(Martin Luther, from LW 24:249 as quoted in Faith Alone: A Daily Devotional, ed. James Galvin)