I wrote this on a pastors forum, and thought it might be of interest to some here as well:
The teaching authority of elders/pastors is always derivative from their concord with the Word of God. This was true from day one of the church. Before the canon was established, the concern was with the authentic apostolic nature of the message brought by a elder/pastor. Of course in the early days this was established by those who were in direct contact with the apostolic churches - those founded by and established upon the teaching of the apostles. This version of "apostolic succession" we all should heartily agree with. Those churches which are in accord with the teaching of Jesus and his apostles are true churches. Those who deviate widely from this teaching are not. This gave rise to the importance of the bishop in the early church - he would be the one to establish sound doctrine. When there was controversy between bishops - this gave rise to councils which deliberated upon this teachers - with the debate hinging upon the teaching of the Bible. The canonization process was of great import as to determine the apostolic witness - the inspired writings vs. heretical teachings (be they from Marcion, Valentinus, etc). The church "recognized" the canon as what it already was - the inspired Word. The canon did not derive its authority from the church's ruling...
During the reformation(s) of the late medieval and early renaissance periods, the concern was to return to the sources (ad fontes) of Christian faith, namely the witness of the New Testament. Where the church was currently deviant from the teaching of the NT, it should be "reformed" - The clear teaching of the Bible should set the course for the churches as it is the authority upon which the church is established...only upon the foundation of the Scriptures can an elder/pastor "teach with authority." The formal principle of the reformation, that of Sola Scriptura - that each persona can read and interpret Scripture, is what McGrath is calling Protestantism's Dangerous idea. It allows all manner of goofy and sinful teaching to be put forth in "the name of being biblical" which no other authority to adjudicate. But the fracturing of the church by heresy did not come with Protestantism, having a guy with the hat on does not guarantee anything. There have been heretics throughout history both pre and post reformation and the church has always had to clarify biblical orthodoxy. The reformation had to wrestle with the question. "What if the guy in the hat gets it wrong?" - Of course the rest has been history.
I both love and hate some of the realities of Protestantism. There are a bunch of goofy interpretations and spins on the Bible, but yet basing the authority in a sinful man's ruling is no better path. This is why someone's belief "ABOUT" the Bible is of great importance. You cannot even debate in council - or on a forum :) - if someone who does not hold to the authority of the text. At least we can wrestle under the text, if the text has authority. If one does not believe in the authority of the text, one will say "it is all hermeneutics, all interpretation" - that there is no definitive meaning to the text. This is why the issue of biblical authority AND hermenuetical outlook are so important. If someone can make up "trajectories" to speak beyond the Bible, they will eventually err far from course.
Right authority ultimately comes only from GOD, we derive that authority from the book whose author is the same. The early church leader's authority stood only upon the word of Jesus and the apostles - this we have preserved for us and our children in the New Testament. Without this, there would be no rule to test doctrine...Of course Rome disagrees, for they have an oral tradition that lives through the magisterium. They claim that the teaching ministry of the Roman church has never contradicted Scripture...I find this somewhat ridiculous and thus remain a Bible guy.