TORAH SHEBALPEH------infallible

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The problem is, the issue is not whether humans are fallible. Of course they are. The issue, rather, is whether Torah shebal peh c”v contains any of those human errors. And neither Mesechta Horios nor the Korbon Chatas have anything to do with that.

The Torah shebal peh of Chazal does not contain any errors. Just as we are obligated to believe that Torah shebiksav is correct, we are obligated to believe that Torah shebal peh is correct. Both are Mipi Hagevurah, and that includes not only the Halachos but also the drashos and peirushei hepesukim of chazal. Here is what the Drashos Haran, says on that issue:

"Just as we are commanded to follow their conclusions [i.e. chazal] regarding the laws of the torah so to we are commanded to follow them regarding traditions and theology (deos) and the way to darshon the pesukim, whether it is regarding a mitzvah or not, and a Jew who veers from their words, even regarding what is not relevant to a mitzvah, is an apikores and has no share in the world to come." (Drashos Haran, #5)

This means even if your actions follow according to their instructions, if you do not believe in the theology or the Deos or the interpretations of the pesukim that Chazal derived, you are an apikores, because you deny Torah she bal peh.