What I am suggesting in Return to Rome is that the Nicean orthodoxy offered by the Puritan divines was only possible because they had the benefit of a Spirit-directed Magisterium that had secured this orthodoxy as normative over 12 centuries prior to the Westminster Confession of Faith. (reference)
Converts (or in this case, reverts) to Roman Catholicism tend to adopt a view of history that is rosey at best, and grossly anachronistic at worst. High language about the “Spirit-directed Magisterium” sounds great in academic circles, as long as it never has to deal with the harsh, messy facts of history. But we surely have the right to ask, “just how did this Spirit-directed Magisterium produce Nicene orthodoxy?” There is this little problem of history in the way: Rome was not in charge at Nicea. In fact, Rome had next to nothing to do with the Nicene definition, and in fact, it was Alexandria, in the following decades, even in the face of Roman capitulation to the rise of Arianism, that stood firm for the Nicene formulation, and that against the entire weight of the “formal” church of that day. Did the Spirit-directed Magisterium move to Alexandria for a few decades in the middle of the fourth century? And if this Spirit-directed Magisterium is not to be equated with Rome itself at that time, why should it be today?
Of course, if Rome gets to take credit for Nicea, does she take credit for Nicea II and its incredible mishandling of Scripture? For the many errors of the medieval period, or the promotion of the Malleus Maleficarum? How about the theology behind the Inquisition? Was that part of the Spirit-guided Magisterium, too?