C.F.W Walther on the Proper Distinction of Law and Gospel

No gospel element, then, must be mingled with the Law. Anyone explaining the Law shamefully corrupts it if he adds grace to it—the grace, loving kindness, and patience of God who forgives sin. That person would be like a nurse who fetches sugar to sweeten bitter medicine, which the patient dislikes. What is the result? Why, the medicine would not work, and the patient would remain feverish. In order to retain its strength, the medicine should not have been sweetened. A preacher must proclaim the Law in such a way that nothing in it is pleasant for us lost and condemned sinners. Any sweet ingredient injected into the law is poison. It renders this heavenly medicine inactive. It neutralizes its effectiveness. (Thesis VI)