It{The church} is (as St. Paul says) a pillar and bulwark of the truth [I Tim. 3:15]. It stands firm (he says) and is a bulwark and sure foundation. It is not a bulwark of falsehood and lies, but a bulwark of truth, neither lying nor deceiving; it has no truck with lies. But whatever wavers or doubts cannot be truth; and what would be the use or need of a church of God in the world if it wanted to waver or be uncertain in its words, or wanted to say something new every day, now asserting this, now rejecting that? Moreover, of what use would a God like this be, who wanted to teach us to waver and to doubt—just as the theology of the papists teaches that one must doubt grace? But enough has been written about that. Even if the papists had won in everything else, they still lose this major point when they teach that we must doubt the grace of God if we are not already worthy enough through our own satisfaction or merit or the prayers of the saints. That is the purpose of their books, letters, seals, convents, monasteries, and even of their tonsures and masses.
Because they teach reliance on works and doubt—indeed, they cannot do otherwise—it is quite certain that they must be the devil’s church. For there are not, and could not be, more than these two ways: the one which relies upon God’s grace, and the other which builds on our own works and merit. The first is the way of the ancient church, of all the patriarchs, prophets, and apostles, as Scripture testifies. The other is the way of the pope and his church, and that is something no one, not even Harry and all the devils in hell, can deny. (Luther’s Works, v.41, p.213)
Picture: The Risen Christ stained glass window at History Trinity Lutheran Church, Souland Market, St. Louis MO