I think the Orthodox Christian (a member on this forum) quoting John Calvin is priceless. We share many similar beliefs with other Christians if we only take time to recognize it. Heady discussions are good but not for everyone.
Yours in the Lord,
jm
The Orthodox position that "the Holy Spirit will lead you into all the truth" applies to the church councils, and therefore what the councils decided is the correct interpretation, is I think suspect. One example is that the tradition of facing East while praying is a suspicious interpretation of scripture, and I certainly don't stake any value on it. There are other traditions that I think are either wrong or irrelevant.
It seems to me that the Catholic position does not agree with material sufficiency of scripture, because the scripture itself is not sufficient to them. He says his idea of material sufficiency is scripture plus the magisterium interpretation. Therefore the Catholic cannot rely on scripture itself, but must lean on the magisterium for truth.
Now, there are certain traditions that are necessary, and are supported by the scriptures themselves, at least by implication. One such tradition is the scope of the canon of scripture. This one is necessary for determining what is inspired scripture versus what is not. Other traditions might be helpful, but are not necessarily needed for correct interpretation for faith and practice.
The weakness in the Protestant position, or reformed position, is that if people aren't very familiar with all scripture, it is easy for people to take scripture out of context and come up with false conclusions, and there are many Protestant cults and heresies as a result of this. So the Protestant position requires that every person take responsiblity for his own knowledge of scripture in order to discern correct interpretation. One of the problems for Christians in every denomination is that the teaching leader might have false interpretatons that propagates to the people who hear him. When people realize this, it drives them to study the scriptures for themselves. So this might be a strength for Protestantism.
Even in Protestantism there are traditions that may not be correct. Certainly there are false ideas in various specific denominations. I think it is both good and important to gain knowledge of early church fathers' interpretations of scripture, not for absolute correctness, but to examine their ideas and see if scripture supports them. Equally, we should be examining ideas from all different denominations to help us get what scripture may be saying to us.
TD
P.S. One more thing I noticed, is that the Catholic debater (William) misunderstood the Protestant's position in this way: The Protestant talked about the internal evidence of the canon in the canon we have today, in addition to the councils following Christ in establishing it. But William's premise was starting from nothing, to determine what the canon is from no canon at all. It is interesting that no one saw this difference in the two positions, and William's misunderstanding.