This is from p. 423 of volume 3 of Pieper’s Christian Dogmatics:
With regard to the orthodox character of a church body note well: (1) A church body is orthodox only if the true doctrine, as we have it in the Augsburg Confession and the other Lutheran Symbols, is actually taught in its pulpits and its publications and not merely “officially” professed as its faith. Not the “official” doctrine, but the actual teaching determines the character of a church body, because Christ enjoins that all things whatsoever He has commanded His disciples should actually be taught and not merely acknowledged in an “official document” as the correct doctrine. It is patent that faith in Christ will be created and preserved through the pure Gospel only when that Gospel is really proclaimed. (2) A church body does not forfeit its orthodox character by reason of the casual intrusion of false doctrine. The thing which the Apostle Paul told the elders of Ephesus: “Also of your own selves shall men arise speaking perverse things to draw away disciples after them” (Acts 20:30), came true not only in the Apostolic Church, but also in the Church of the Reformation and will occur in the Church to the Last Day. A church body loses its orthodoxy only when it no longer applies Romans 16:17, hence does not combat and eventually remove the false doctrine, but tolerates it without reproof and thus actually grants it equal right with the truth.
I admit that we have seen great zeal in the ELS to apply Romans 16:17, even bypassing the proper steps given in both Scripture and the synod guidelines. Does such zeal confirm the ELS as an orthodox church body? (Or is it that we have retained fellowship with our sister synod in Wisconsin? Sorry, couldn’t resist. Yet an answer may still be helpful.)
Note the basis that Pieper gives for application of Romans 16:17: “the true doctrine, as we have it in the Augsburg Confession and the other Lutheran Symbols.” This leads to the question: what is a Lutheran Symbol? At Bethany Seminary, our Symbolics class covered the Book of Concord. We did not examine the local doctrinal statements of the ELS or any other synod, except to compare their teaching with that of the Book of Concord, to see how they measure up.