C.F.W. Walther on Law and Gospel

"The...difference between the Law and the Gospel relates to the persons to whom either doctrine is to be preached.  The persons on whom either doctrine is to operate, and the end for which it is to operate, are utterly different.  The Law is to be preached to secure sinners and the Gospel to alarmed sinners.  In other respects both doctrines must indeed be preached, but at this point the question is: Which are the persons to whom the Law must be preached rather than the Gospel? and vice versa.

"1Tim 1:8-10 [We know that the law is good if one uses it properly. We also know that law is made not for the righteous but for lawbreakers and rebels, the ungodly and sinful, the unholy and irreligious; for those who kill their fathers or mothers, for murderers, for adulterers and perverts, for slave traders and liars and perjurers — and for whatever else is contrary to the sound doctrine (NIV)]: As long as a person is at ease in his sins, as long as he is unwilling to quit some particular sin, so long only the Law, which curses and condemns him, is to be preached to him.  However, the moment he becomes frightened at his condition, the Gospel is to be promptly administered to him; for from that moment on he no longer can be classified with secure sinners.  Accordingly, while the devil holds you in a single sin, you are not yet a proper subject for the Gospel to operate upon; only the Law must be preached to you.

"To poor, sad-hearted sinners - I repeat it - not a word of the Law must be preached...On the contrary, to such a person the preacher must say: "Do but come! There is still room for you! No matter how great a sinner you are, there is still room for you.  Even if you were a Judas or a Cain, there is still room.  Oh, do, do come to Jesus!"  Persons of this kind are proper subjects on whom the Gospel is to operate."

-from God's No and God's Yes: The Proper Distinction between Law and Gospel a book published posthumously via manuscripts from lectures he delivered between Friday, September 12, 1884, and terminated Friday, November 6, 1885.  Our excerpt is from the second evening lecture delivered September 19, 1884.  The full 39 lectures are available online here.