Here's some more free stuff.Out of the quotes that I found and cited, these three could use fuller quotations:
1) Timothy Wengert notes in Reading the Bible with Martin Luther that in Luther's lectures on 1 John in 1526-1527, Luther remarked that "it is very rare that there are pure teachers in the church. Only Scripture is pure." I have trouble finding more of the passage.
Wengert cites to WA 20:745, 2–3 (from the copy of the lecture by Georg Rörer, not used by LW 30:295).
I finally found a minute to look up LW 30:295, a task... I'm compelled to point out... isn't really all that hard in our current time in history. What is more confusing is understanding how Luther's words came to be in the form they're in now. Some are fairly simple: Luther wrote them. In his sermons and lectures though, more often than not, Luther's words were written down by those who heard him say them, and later turned into a written artifact.
When Wengert says, "from the copy of the lecture by Georg Rörer, not used by LW 30:295" he's saying this particular lecture was heard and written down by different people. In this instance, Georg Rörer took down notes and formulated an account of what Luther said, but the editors of LW chose to not use his account for their English translation. The version LW used is "attributed to Luther's associate Jacob Propst in Bremen." The editors of LW point out that some material in Rörer's version is not found in Propst, and also some material found in Propst is not in Rörer's version. Because Propst's version had been published previously (1708), LW chose to use Propst, but does not disparage Rörer's version.
When one visits the context of LW 30:295, there's obvious overlap between Rörer and Propst. Luther is commenting on 1 John 4:11. The article that Satan is trying to take away is that Christ is our complete expiation. The monks, in essence by their emphasis on works, actually deny the work of Christ. If they do not repent, they will be condemned. This is something John Wycliff figured out long ago about the monks (which surprises Luther that Wycliff saw this). Then comes Rörer's account: "it is very rare that there are pure teachers in the church. Only Scripture is pure." When Luther calls Cyprian an "Anabaptist" it's because Cyprian held people baptized by heretics must be rebaptized. Luther's comment about Augustine is that even though Augustine condemned this stance by Cyprian, that he was a martyr forgives him this error. Luther then takes some shots at the Franciscans works righteousness, as well as Gregory and Bernard who founded works righteousness monasteries. All these examples have the common denominator of a denial of justification by faith apart from works. Therefore, as far as I can ascertain what Rörer is getting at is that the "pure" teachers of the church are those who taught justification by faith apart from works, a rare occurrence.
Notice what Wengert says about the context:
Another example of the same skepticism came in Luther’s lectures on 1 John in 1526–27. Again, the context made clear that he was not eliminating other authorities but actually discussing how to appropriate such authorities into the interpretation of Scripture. He began with the remark that “it is very rare that there are pure teachers in the church. Only Scripture is pure.” Luther did not, however, exclude other authorities, as if he were saying that Scripture alone were authoritative. The purity of Scripture had specifically to do with justification by faith as opposed to monastic vows—that is, “Was Christum treibet!”
Wengert's comments are a little confusing to me. I'm not sure the context makes it "clear" that Luther "was not eliminating other authorities," for, other than Wycliff, everyone mentioned is criticized by Luther! This context, as far as I can tell, doesn't discuss the nature of secondary authorities other than Scripture, so again, I'm not entirely sure what point Wengert is trying to make from the context. Not far later Luther quotes Augustine positively (LW 30:298, 299). True though, in this context, I think Wengert is right that Luther links the purity of Scripture to the purity of justification by faith alone apart from works.