John Calvin believed that preaching is dead when Ministers of the Word rely solely on ornate preaching. A Minister of the Word that is filled with the Holy Spirit ought to preach in accordance with the Spirit: namely, in Power.
Calvin commenting on 1 Corinthians iv.20 (For the kingdom of God is not in word, but in power.) — As the Lord governs the Church by his word, as with a sceptre, the administration of the gospel is often called the kingdom of God. Here, then, we are to understand by the kingdom of God whatever tends in this direction, and is appointed for this purpose—that God may reign among us. He says that this kingdom does not consist in word, for how small an affair is it for any one to have skill to prate eloquently, while he has nothing but empty tinkling [sound of tinkling in the air]. Let us know, then, a mere outward gracefulness and dexterity in teaching is like a body that is elegant and of a beautiful colour, while the power of which Paul here speaks is like the soul. We have already seen that the preaching of the gospel is of such a nature, that it is inwardly replete with a kind of solid majesty. This majesty shows itself, when a minster strives by means of power rather than of speech—that is, when he does not place confidence in his own intellect, or eloquence, but, furnished with spiritual armour, consisting of zeal for maintaining the Lord’s honour—eagerness for raising up of an invincible constancy—purity of conscience, and other necessary endowments, he applies himself diligently to the Lord’s work. Without this, preaching is dead, and has no strength, with whatever beauty it may be adorned. Hence in his second epistle, he says, that in Christ nothing avails but a new creature (2 Cor. v. 17)—a statement which is to the same purpose. For he would have us not rest in outward masks, but depend solely on the internal power of the Holy Spirit.