An ordinary sin-offering is brought by an individual who accidentally performs an act forbidden by the Torah. As we have learned, Masechet Horayot discusses the passages in Sefer Vayikra (4:1-26) that teach about three exceptional sin-offerings:
The Mishnah on today’s daf (=page) teaches that the cases of the High Priest and the High Court are parallel. When the High Court rules erroneously and that decision is acted upon by the majority of the Jewish community, the High Court will be obligated to bring a sin offering on behalf of the community. Similarly, when the High Priest made a decision on Jewish law in error and acts upon his ruling he will bring a unique sin offering. In both of these cases it is not the forbidden act itself that creates an obligation to bring the sacrifice, rather it is specifically the mistaken ruling that precipitates the forbidden act that creates that obligation.
The Gemara brings a source for this law from the passage (Vayikra 4:13) that teaches yishgu, ve-ne’elam davar – that a mistake was made because something was “hidden” or misunderstood – therefore we conclude that a mistaken action will not obligate the unique sacrifice, only an action that is caused by a mistaken legal decision.
Tosafot point out that the Gemara has already taught many rules from which it is clear that the sacrifice will be brought only if an erroneous decision was made. For example, if no legal decision was involved, how could the court be obligated to bring a sacrifice for a forbidden act done by the majority of the community? If the court played no role at all Tuvia hatah ve-Zigud mingad?! Is there any logic to say that Tuvia sinned but Zigud should receive lashes!? Tosafot answer that without this passage we may have thought that it would not have been the court, but the community who would be obligated to bring the sacrifice. The pasuk (=verse) quoted by our Gemara teaches that it is the court who will bring the sacrifice, but only in a case where they played a role, i.e. where the erroneous decision was theirs.