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)