To be sure, the orthodox Church outwardly often bears a very humble form. And this can, even for Christians, when they are not on their guard against their flesh, become an inducement to be ashamed of their Lutheran Church and to hanker after sectarian churches, standing there in outward splendor. But, we ask, what is the reason? Why does the Lutheran Church outwardly often appear so decidedly in the form of a servant? Is it not just because of its faithfulness to God's Word? Is it not the circumstance, that the orthodox Church primarily in its doctrine is serious about God's Word; that it, because of God's command, does not remain silent in the presence of error, but condemns it; that it does not deal traitorously with the Divine truth, does not look upon truth and error as having equal rights? Is it not, furthermore, also a fact that the orthodox Church takes the Word of God seriously in regard to this life, that it impresses upon the poor, as upon the rich, that all who claim the Name of Christ have the duty to depart from iniquity, and that whoever conforms to the world will also be lost with the world? Yes, that is the practice of the orthodox Lutheran Church, and therefore it must often bear a servant's form. Would it not be disgraceful if we would be ashamed of this Church because of its outward lowliness, which under these circumstances is an honor for it? Would it not be disgraceful if we would rather want to hold to heterodox churches, because outwardly they are more attractive and of greater value in the eyes of the world? By what means have the heterodox churches, for the most part, purchased this outward greatness and honor before the world? By their unfaithfulness to God's Word. They deny the truth by not insisting on the exclusive validity of Divine truth, but honoring all kinds of opinions, they flirt with the wisdom of this world, and its godless manner of life.
…Luther confesses of himself, and of the whole church body named after him: "No man can deny this, that we have the ministry and God's Word pure and rich, that we use and teach it diligently, without any addition of our own new human doctrine, just as Christ commanded, and as the Apostles and all Christendom have done. We invent nothing new but rather hold to and remain with the old Word of God, as the old Church had it. Therefore, with it we are the true old Church, a one-of-the-same-kind Church, which teaches and believes the one Word of God. Therefore the papists again blaspheme Christ Himself, the Apostles, and all Christendom, when they call us Modernists and heretics. For they find nothing about us except only the same old things of the Ancient Church, and that we are like it and one Church with it." (Against Hans Wurst, 1541. E.A. 26,14.)
Luther states further: "The impurity of doctrine which is not God's Word, or is without it, is such a poisonous evil thing that even if St. Peter, yes, an angel from heaven would preach it, it would still be accursed, Gal. 1:8. Therefore false teachers and Anabaptists or fake masters of the Sacraments cannot be or remain in the Church, as Psalm I says, for they not only undermine the life, which the Church must bear, especially where this goes on under cover, but also the doctrine is undermined, which must openly be bright and shine, so that the life can be regulated according to it." (E.A. 26,37.)
from Franz Pieper, 'The Distinction Between Orthodox and Heterodox Churches'Read More