At times though, it gets a bit odd. For example, when Genesis says "God said such and such to Abraham" Luther will frequently argue that Abraham didn't hear a voice or something, but rather that Shem or some other Patriarch spoke to him. Since the Holy Spirit was speaking through them, it was in fact the Word of God.
My question (beyond the fact that this doesn't make much sense exegetically) is what's the difference? In other words, how does it make it better that the Holy Spirit is inspiring the Patriarch to speak some sort of external Word to Abraham, rather than the Holy Spirit speaking within Abraham? The functionally the two are no different.
Also, I see the problem with Medieval popes or with Thomas Munzer thinking that their own thoughts are identical with that of the Holy Spirit, but I don't not see the difficulty or the violation of Luther's principle by positing that the Holy Spirit spoke to Abraham in such a way that he individual heard it without a medium. For revelation to take place, you have to posit that happening at some point.