From the Word
And the Spirit is the witness, because the Spirit is the truth.
1 John 5:7, RSV
John employs the word “witness” in connection with the thought of preaching; it is a word which he frequently uses. In the beginning of his gospel, where he speaks of John the Baptist, he says, “The same came for a witness, that he might bear witness of the light.” So in the use of the words “witness” or “bearing witness,” we are to understand simply the public preaching of God’s Word. Christ says, that the Holy Spirit shall bear witness of him; that is, it shall publicly fill the ministerial office. This is God’s own witness to his Son.
This witness, Christ himself ordains, shall ever go forth, and remain in the Church. To this end Christ himself called and gave the Holy Spirit to the apostles and their successors, ministers, preachers, and teachers. For the sake of the uninstructed masses and the constantly rising young who, as yet in ignorance of the Word, need admonition — for the sake of these, the Spirit must bear public witness or administer the preaching office that they, too, may learn to know the grace of God manifest and given us through Christ, and that God’s wondrous works may be publicly recognized and extolled by us in opposition to the devil and the world.
Wherever such witness is borne, there certainly will be some fruit; the witness never fails of effect. Some surely will be reached; some will accept and believe it. Since it is the witness of the Holy Spirit, he will be effective, producing in us that to which John refers when he says we are the children of God, and have the victory and eternal life. The Word and faith are vitally related. They are inseparable. Without faith, preaching will be fruitless; and faith has origin in the Word alone. Therefore, we should gladly handle and hear the Word. Where it is, there is also the Holy Spirit; and where the Spirit is, there must be at least some believers. If you have already heard the Word and obtained faith, it will always continue to strengthen you as you hear it. For the Spirit, as Christ says, breathes where he will, and touches hearts when and where he knows them to be receptive.
Luther, Martin, and John Sander. Devotional Readings from Luther’s Works for Every Day of the Year. Augustana Book Concern, 1915, pp. 177–78.