Heterodox churches do not exist by the will of God, Matt. 28,20, but against His will, Jer.23,29-40; 1 Cor.3,15-17. God permits them to exist partly to prove the faith of His true disciples, 1 Cor. 11, 19, and partly to punish the indifferentism, ingratitude, and infidelity of the ungodly, 2 Thess. 2, 11. 12.
Hence Christians should view the existence of heterodox churches not with indifference, but with horror, since every error is an offense (σκάνδαλον), which not only provokes God to anger, Deut. 32, 5. 6; 28, 15-68, but also endangers the salvation of all who are brought into contact with it, 1 Cor. 15, 33; 2 Tim. 2, 16. 17.
Nevertheless true believers may be found even in heterodox churches, not inasmuch as they are heterodox, - for falsehood always opposes itself to saving faith, - but inasmuch as by the grace of God they still retain the fundamentals of the Gospel.
Our Savior Himself, while denouncing the religion and worship of the Samaritans, John 4, 22, still acknowledged the true discipleship of individual believing Samaritans, Luke 17, 16; 10, 33. So also Luther, though he condemned the Papacy as an institution founded by the devil, still recognized true believers (the baptized children; adults who adhered to the sola gratia against the teachings of the Pope) also in this corrupted Church. Similarly the great Reformer held that there were true believers among the followers of Zwingli and Calvin because they adhered to them in ignorance. St. L., IX, 44.
The confessional Lutheran Church, though ever insisting upon the prerogative of being the true orthodox Church, has never identified itself with the una sancta ecclesia, extra quam nulla est salus, but bas always taught that the Church Universal is the communion of all believers who put their hope of salvation alone in Christ's vicarious atonement. (Cp. Walther, Kirche und Amt., pp. 95-113; 160 ff.) Dr. Walther writes: "Whoever binds salvation to membership in any visible Church annuls the article of justification by grace alone, through faith in Christ."