“You must distinguish between the genuine Christian Church, the true church, and the church which presumes to be the church but is not. The false church has only the appearance, although it also possesses the Christian offices. Even a knave is able to baptize, read the Gospel, go to the Sacrament, and recite the Ten Commandments. All this is and remains proper, but he remains a vile knave and is not to be called a Christian or the Christian Church. No, we say that he is found in the Christian Church just as mouse droppings are found among the pepper or cockleburs among the grain. They merely help to fill the bushel. A body may possess fine, sound, and useful members which man can employ for his various needs; but that same body may also contain perspiration, secretion from the eyes, nasal mucus, scabs, abscesses, and other filth.
All the latter are found on the human body together with ears, stomach, heart, fingers, and eyes. But filth is still part of the body, even though it stinks. Thus the heretics, the false teachers, or the ungodly in the church are not its natural and genuine members but the filth which the body exudes. Consequently, it is true that no one will ever preach the truth unless he is in the Christian Church. To be sure, he can preach; but that is not enough. He must also have the Holy Spirit, preach the truth, and lead a decent life. And this he cannot do unless he is a true member of the Christian Church” (Luther’s Works, v. 23, p. 286-287).