Now observe, my dear friend, what a wonderful thing this is: we who teach God’s word with such certainty are so weak, and in our great humility so timid, that we do not like to brag that we are God’s church, witnesses, servants, and preachers, and that God speaks through us, etc. And yet, we do not doubt it, since we are certain to have and to teach his word. Such timidity stems from the fact that we earnestly believe God’s word is such a noble and majestic thing that we regard ourselves far too unworthy of its being spoken and done through us who are still creatures of flesh and blood. But our adversaries, the devils, the papists, the sects, and all the world, are confident and intrepid, asserting with great holiness and arrogance, “Here is God, we are God’s church, his servants, prophets, and apostles.” It is just like every false prophet has always done, so that even Harry-wurst dares to boast that he himself is a Christian prince. But the true sign of the true holy church has always been humility and fear in the word of God, whereas lust and wantonness in innovating have been the true signs of the devil—something that becomes quite evident from the pope’s decretals. (Luther’s Works, v.41, p.217-218)

This we say about doctrine, which must be pure and clean, namely, the dear, blessed, holy, and one word of God, without any addition. But life, which should daily direct, purify, and sanctify itself according to doctrine, is not yet entirely pure or holy, so long as this maggoty body of flesh and blood is alive. But as long as it is in the process of purification and sanctification, being continually healed by the Samaritan and no longer decaying in its own impurity, it is graciously excused, pardoned, and forgiven for the sake of the word, through which it is healed and purified; thus it must be called pure. This is why the holy Christian church is not a whore or unholy, because it continues to hold to and remain with the word (which is its holiness) without blemish and with strength. “You are already made clean (says Christ in John 15 [:3]) by the word which I have spoken to you,” not on your own account. (Luther’s Works, v.41, p.218)

If the word were to be sinful or untrue, after what would or could men guide their lives? Then, no doubt, a blind man would lead a blind man, and both would fall into the pit [Matt. 15:14]. If the plumb line or the T-square were false or crooked, what kind of work would or could the master-builder produce? One crooked thing would make the other crooked, without limit or measure. Life too can be sinful and untrue in the same way—unfortunately life is indeed very untrue—but doctrine must be straight as a plumb line, sure, and without sin. Therefore nothing must be preached in church except the sure, pure, and one word of God. Where that is missing, we no longer have the church, but the synagogue of the devil [Rev. 2:9], just as a godly wife (an example the prophets always use) should not listen to any other word in her house or in her bed than that of her husband, and if she does listen to the word of someone who does not belong in her husband’s bed, she is certainly a whore. (Luther’s Works, v.41, p.216-217)