But that does not address Rinnie’s point. If Christ promised the guidance of the Holy Spirit until the age, why should we think that that guidance would not be given in the development of doctrine in ages past the 4th Century.
If there is fear of imagination corrupting faith, then it was equally possible of it corrupting the faith in the 4th century.
As a matter of fact, it was the Eastern Churches that fell into heresy.
Either we can take Christ at His word or we can’t. We fear our own limitedness but trust in God’s promise.
The century does not matter. Fourth, third, first, tenth it makes no difference. You misunderstand the meaning of the promise of the guidance of the Holy Spirit.
It was not to introduce new doctrines that Jesus Christ somehow neglected to tell us.
It was to help us hold fast to the Truth.
Jesus is the Master, the Teacher.
The Holy Spirit is the Comforter, the Advocate. The Holy Spirit is not with us to reveal new mysteries over time (as if the earlier generations were ‘not ready’).
It is heretics who drive the development of doctrine, the councils acted as a remedial measure to limit the damages and prune out the dross. They were never called with the intention of defining new doctrines, but were often called to fight errors. In early times only heretics thought to define doctrine on their own authority, and we know them by name as the sources of their errors. No Orthodox bishop, not even the bishop of Rome ever tried it. Now it seems to be claimed as a right, and people even organize petition drives to encourage the Pope to name new dogmas.
If you open up to the possibility, even the expectation, that there will be more doctrine and new teachings coming along you potentially place yourself into the hands of heretics and false prophets. You are no better off than the JW’s with their ‘New Light’.
As to your other comments, heresies arose in the east and the west alike. And yes, there were more heresies arising in the east than the west in the early centuries, for it was in the east that the intellectual life and culture was the most advanced at the time, and where most of the Christians dwelled. It was the Orthodox who battled them all, won back the multitudes, endured the persecutions and survived.
We know the dangers, we have seen them all come and go. We have also seen the western church shatter into 30,000 pieces in spite of the confidence it has in itself, all due to this intellectual hubris, this thinking it has the monopoly on ‘the Rock’ and can do as it pleases.