The third use of the law is not the preacher’s to use. Rather, it is the Holy Spirit’s to use. It is the Holy Spirit who uses the law according to all of its uses whenever and wherever it is preached. The third use simply denotes one of several different ways that the proclaimed law functions in the heart of the hearer. This does not mean that the Holy Ghost preaches the third use apart from the oral Word proclaimed and heard. For the law that the Holy Ghost uses is precisely that law that is preached and none other.
Regarding that which is proclaimed by the preacher, one can only conclude that it is the same law that is preached to the Christian and non-Christian alike – complete with all the curses, threats and punishments that always accompany the preaching of the law according to its various uses. That task is left to the Holy Spirit to accomplish as he will wherever the law is preached in its full force. Any attempts to speak of the third use as if it were the preacher’s use are contrary to the intended sense of the Formula. The working of the Solid Declaration must stand unqualified, that “it is just the Holy Ghost who uses the written law for instruction” (Solid Declaration VI:3). Only in this way will one make proper use of the Evangelical Lutheran doctrine of the third use of the law.
– Jonathan G. Lange, “Using the Third Use: Formula of Concord VI and the Preacher’s Task”, LOGIA, Volume 3, Number 1, page 23