Someone asked about the filioque controversy, from the Latin word for "and the Son." Latin has that little trick, adding "que" to a word for "and." The "filio" part is from the word for son or daughter, which we still use as "filial respect" a phrase today chiefly honored by its absence.
I know that Concordia, Ft. Wayne, has promoted Eastern Orthodoxy so much that they have turned out a number of graduates who joined EO immediately after graduation. EO seems to exist in the LCMS as a safe cover or transition point for becoming a Roman Catholic priest. Ft. Wayne graduates tend to be obnoxious, rude, know-it-alls, emulating their favorite OJ professor. Even those who despise Scaer follow his example.
So this matter comes up among Lutherans via the two LCMS seminaries, Ft. Wayne and St. Louis.
The Byzantine or Eastern Roman Empire continued to exist and thrive after the Fall of the Western, European Empire. The Bishop of Rome, now known affectionately as the Pope, asserted his primacy over all other bishops, the "first among equals," which was very annoying to the Eastern Orthodox.
The Emperor Constantine was bolder, calling himself "First of the Apostles."
Creeds are fashioned over time, the Apostles Creed being so early that no one seems to know when it originated. The Nicene Creed was written later, to deal with the Two Natures in Christ.
EO was not happy with "and the Son" being added to the Nicene Creed, a change which happened much later. Rome and Eastern Orthodoxy were estranged at that point and that continued, like a married couple who live a thousand miles apart.
Eastern Orthodoxy had so many bitter, bloody controversies that they fell into an emphasis upon extreme smells-and-bells and flexible dogma. Those mainline ministers who chafe at the short-comings of their denominations and synods are attracted to EO, especially worship with anything-goes doctrine.
Long ago, Jay Webber insisted that I read a book on Melanchthon's discussions with the Eastern Orthodox, that coming from a someone who confessedly knew nothing about Luther except the usual negative drivel. Ft. Wayne at work!
The chap who helped edit Missouri's Lutheran Service Book joined EO as soon as the hymnal was out. He also denounced Justification by Faith at that time (following EO). But, that is no shock - an editor of the NIV Concordia Self-Study Bible, after retiring as a St. Louis professor, also repudiated the Chief Article. In both cases, they wanted to add works to justification, typical of Rome, EO, and ELCA.
Some years ago, I was reading on the Internet when a LCMS pastor wrote, "Sit down everyone and grab a beer. I have joined the Eastern Orthodox Church."
So where are we? I see filioque as a sign that people are being taught and disturbed by Eastern Orthodoxy but not by Biblical Lutheran doctrine. <Sigh> I have to get out my Paul Kelm Luther quote on the hay wagon.
The Lutheran (ELCA-WELS-LCMS-ELS-CLC) seminaries do not teach Biblical doctrine. They openly despise Luther's teaching and the Book of Concord. They gave it away during the Reformation's 500th Anniversary.