Here is the Third Evening Lecture from C.F.W. Walther’s The Proper Distinction Between Law and Gospel.
Before Walther goes on to his second thesis, he takes this lecture to talk about the dangers of mingling the Law with the Gospel.
Walther starts his lecture by talking about the dangers of false doctrine, and how it relates to drinking poison. Both lead to death, one physical, the other spiritual.
“An entire banqueting party drinking from cups containing an admixture of arsenic can drink physical death from its cups. So an entire audience can invite spiritual and eternal death by listening to a sermon that contains an admixture of the poison of false doctrine. A person can be deprived of his soul’s salvation by a single false comfort or a single false reproof administered to him.”
He the makes it clear that the false doctrine he is speaking of is the mingling of God’s Law with His Gospel.
He then spends the majority of this lecture quoting Luther from his commentaries on John, the Psalms, and Galatians, showing who the Gospel is to be given to, namely, the thirsty.
“The doctrine of the Law, then, was given for this purpose, that a person be given a sweat-bath of anguish and sorrow under the teaching of the Law. Otherwise men become sated and surfeited and lose all relish of the Gospel. If you meet with such people, pass them by; we are not preaching to them. This preaching is for the thirsty; to them the message is brought: ‘Let them come to Me; I will give them to drink and refresh them.’ ”