From the Word
6 There was a man sent from God, whose name was John. 7 He came for testimony, to bear witness to the light, that all might believe through him. 8 He was not the light, but came to bear witness to the light.
John 1:6–8, RSV
O, what necessary repetition! First of all to show that this Light is not simply a man, but God himself; for the evangelist greatly desires to preach the divinity of Christ in all his words. If John, the great saint, be not that Light, but only a witness of it, then this Light must be something far different from everything that is holy, whether it be man or angel. If holiness could make such a light, it would have made one of John. In the second place, such a repetition is necessary to resist wicked preachers, who do not bear witness of Christ, the Light, but of themselves. All who preach the doctrines of men make man the light, lead men away from God to themselves, and set themselves up as the true Light, as the pope and his followers have done. He is, therefore, the Antichrist, that is, he is against Christ, the true Light.
This gospel text desires only to testify of Christ and lead men to him, who is the true Light, which lighteth every man coming into the world. Therefore these words, “He was not the Light,” are truly worthy to be capitalized and to be well remembered against the men who set themselves up as the light and give to men doctrines and laws of their own fabrication. They pretend to enlighten men, but lead them with themselves into the depths of hell; for they do not teach faith and are not willing to teach it. Who does not preach the gospel to you, him reject and refuse to hear. But he preaches the gospel who teaches you to believe and trust in Christ, the eternal Light. Therefore beware of everything told you which does not agree with the gospel, as for example eating and drinking, which are necessary for your body, but by no means to your salvation. For this purpose nothing is necessary or of use to you except this Light.
O, these abominable doctrines of men, which are now so prevalent and which have almost banished this Light! They all wish to be this Light themselves, but not to be witnesses of it. They advocate their own fancies, but are silent about this Light, or teach it in a way so as to preach themselves along with it. This is worse than to be entirely silent.
Luther, Martin, and John Sander. Devotional Readings from Luther’s Works for Every Day of the Year. Augustana Book Concern, 1915, pp. 225–26.