Horayot, Chapter Two, Mishnah Two
Mishnah two continues to discuss the anointed high priest who issues an errant ruling.
I) An [anointed high priest] who rendered an errant decision alone and acted accordingly alone, he makes his atonement alone.
II) If he rendered his ruling together with [the court of] the congregation and acted accordingly together with the congregation, he makes his atonement together with the congregation.
III) For the court is not liable unless they ruled to annul part of a commandment and to retain a part of it; and so [it is with] the anointed [high] priest.
A) Nor [are they liable] for idolatry unless they ruled to annul the law in part and to retain it in part.
Section one: If the high priest issued an errant ruling on his own, in other words without the court having taken part in the decision making, and then he acted alone, he alone must bring a bull as a sin offering. This is basically the same rule that we learned in the previous mishnah. It is summarized here in order to offer a contrast with the following section.
Section two: If the high priest ruled in error with the court of the congregation, the sanhedrin, and transgressed together with the rest of the congregation, then he need not bring a special bull on his own. Rather he receives atonement through the same bull that the community brings.
Section three: The language of this section makes it look as if it is a commentary on the previous section, but its content seems independent. The section teaches that just as we learned above in chapter one, mishnah three, that a court is not liable to bring the bull sin-offering unless it ruled to annul part of a commandment but retain the rest, the same is true for the high priest. If he rules, for example, that there is no such thing as Shabbat, he is not liable to bring a bull; but if he rules that a certain forbidden activity is actually permitted on Shabbat, he is liable. These same rules apply with regard to both regular sins and to sins involving idolatry.