Luther proved right again.
Luther said, in effect, Christian doctrine is whatever I believe Scripture convicts me of, today.
+Francis, and his supporters, say "Catholic doctrine is whatever I say it is, today".
The Mormons say, "LDS doctrine is whatever the living prophet of the church says it is, today."
Professor Rist is saying, along with St Vincent of Lerins, is that Catholic doctrine is whatever the Church has always taught, and conclusions which flow from it logically. And the great counter-Reformation Doctor Ecclesiae, St. Robert Bellarmine, said pretty clearly that a Pope who was a contumacious heretic had surrendered his office and ought to be deposed by the bishops.
Still sure what Prof. Rist is saying backs up Luther?