Law and Gospel
This book contains one of the best expositions of this distinctive in Lutheran preaching. The book covers everything from "how to preach" to "doctinal errors to avoid", although not sorted out as that.
The text was originally a set of informal weekly lectures by the president of Concordia Seminary (in St. Louis, Missouri). (Incidently, that president was also president of The Lutheran Church Missouri Synod). Since topics could run over from one night to the next, there are often even preludes inserted in the topic sequence.
At the time of the lectures, The Lutheran Church Missouri Synod contained mostly German immigrants to the USA and the accepted language of the church was German. So this talks were in German. They were not recorded at the time, but the students did keep copious notes (and students in the past seem to have remembered talks and lectures far more accurately than today). These notes were gathered together later and from them was created this book.
First printed in German, it was translated in the early years of the 1900s in English as The Lutheran Church Missouri Synod began to change from German to English (that change accelerated as a result of the World Wars, but was not completed until the 1950s!)