I choose that particular passage because brings together the two areas of discipline in the early church, doctrinal and moral. However a cursory examination of the letters of the New Testament reveals that almost every writer is dealing with the same set of issues: thus Paul in I Corinthians 5-6 is dealing with moral issues, whilst in Galatians he is jumping up and down about doctrine. In I John he is concerned with moral issues, whilst in 2 John he does doctrine. Even Hebrews finds time to throw in a reference to moral issues (Heb 13 v 4) after the extensive doctrinal message. So it's an element in the New Testament that we need to take seriously....

I'm not quite sure how to understand your raising of the fact that the Eastern Church regards Revelation as a mystery. If you're trying to argue that therefore we can ignore its clear teaching, I think you are on very thin ice. I totally agree that we need to resist the temptation to build a major doctrine out of a few verses in Revelation, but to attempt to dismiss a passage because it is in Revelation when it merely reiterates material that is expressed in other ways in the New Testament seems unwise. At some point we have to take seriously the warning:

And if anyone takes words away from this book of prophecy, God will take away from him his share in the tree of life and in the holy city, which are described in this book. Rev 22 v 19.