God works through this means (i.e. the preaching and hearing of His Word). He breaks our hearts and draws us to Him. Through the preaching of the Law, a person comes to know his sins and God’s wrath. He experiences in his heart true terrors, contrition, and sorrow. Through the preaching of, and reflection on, the Holy Gospel about the gracious forgiveness of sins in Christ, a spark of faith is kindled in him. This faith accepts the forgiveness of sins for Christ’s sake and comforts itself with the Gospel promise. So the Holy Spirit (who does all this) is sent into the heart.
The preacher’s planting and watering and the hearer’s running and hearing would both be in vain and no conversion would follow it if the power and effectiveness of the Holy Spirit were not added. The Spirit enlightens and converts hearts through the Word preached and heard. So people believe this Word and agree with it. Neither preacher nor hearer is to doubt this grace and effectiveness of the Holy Spirit. They should be certain that when God’s Word is preached purely and truly, according to God’s command and will, and people listen attentively and seriously and meditate on it, God is certainly present with His grace. He grants, as has been said, what otherwise a person could neither accept nor give by his own powers. For we should not and cannot always judge from feeling about the presence, work, and gifts of the Holy Spirit, as to how and when they are experienced in the heart. They are often covered and happen in great weakness. Therefore, we should be certain about and agree with the promise that God’s Word preached and heard is truly an office and work of the Holy Spirit. He is certainly effective and works in our hearts by them. (Formula of Concord, Solid Declaration, Article II, para.54-56; Concordia: The Lutheran Confessions, p.530)
The reader should take special note of what is said about judging from feelings about the presence and working of the Holy Spirit. Too many people mistake what is simply strong emotion for the movements of the Spirit. In a climate that breathes, eats, and speaks feelings first as the measure of all doctrine and practice, indeed, of religion in any sense, this caveat is especially valuable. We need to judge things by the objective Word alone. That is our only sure ground.
The sermon is not twenty minutes (or more) of droning, cute stories about family trips to the Rockies, or the warmed-over jokes and anecdotes we all get in our email. It is where God exercises His power through His Word on the hearts of the hearers (and the preacher.) It is an encounter with the living God, as indeed any occasion we read or study God’s Word is. Do we treat it as such? Would fewer people nod off during the sermon if they kept these thoughts from the Formula of Concord in mind, or knew them in the first place?