Kinds of Changes
There have been many changes in the Churchand in doctrineover the centuries. This would not be a concern except that certain Christian groups latch on to one particular formulation and claim it represents the true church for all ages. Certainly infallible truthcan't change. Therefore, anything that has changed is not in the category of infallible truth.
There is, of course, no problem with customs changing, or with applying Christian truth to new situations from generation to generation.
Of note is that doctrine on key topics changed before finally solidifying. In the very turbulent centuries during which the Trinity was discussed and argued about, there were multiple councils with bishops on both sides of the Arianism issue. And there were many other variations which I won't discuss. Finally, with the emperor's strong-armed influence, the Council of Nicea decreed the Nicene Creed.But it didn't stick, and after another turbulent half-century the Council of Constantinople decreed the Nicene-Constantinopolitan creedwhich is the final form (except that Catholics much later added the filioque clause).
If you were trying to prove that the Holy Spirit worked through the bishops in determining this doctrine, you would have to ignore what really occurred. There was strong influence by the emperor. The popes seemed uninterested. The behavior of Bishops was very ill-mannered and unbecoming — there were even assassinations of bishops by bishops.
So how do we explain the various strange goings-on in the Church over the centuries? Even the apostles had flaws and wavered in their support of truth (Peter's pulling away from the Gentiles when pressured by Jews.)Shouldn't we expect a much higher standard of behavior from these Church leaders than we observe?
My solution to all these kinds of questions is to focus on the apostolic Church and to use it as the model for judging Churches and Christians...