Midrash sur Le Lévitique 4:13

1) (Vayikra 4:13): "And if (the whole congregation of Israel err"): "And if" "adds" (i.e., is secondary) to what precedes, (the section of the high-priest), so that if the bullock of the high-priest and the bullock of the congregation are awaiting (sacrifice), the first takes precedence in all services.

2) "the congregation of Israel": I might think the entire congregation is being referred to; it is, therefore, written here "congregation" and elsewhere (Numbers 35:24 and Numbers 35:25) "congregation." Just as a "congregation" there refers to beth-din, so, "congregation" here refers to beth-din. If so, I might think that just as "congregation" there refers to (a beth-din of) twenty-three, so, "congregation" here. It is, therefore, written: "the congregation of Israel." — the congregation which is "distinctive" in Israel. Which one is that? The Great Sanhedrin (of seventy-one), which sits in the lishkath hagazith (the "chamber of hewn stone").

3) I would think that if one of them (the beth-din) were a convert or a mamzer or a Nathin or an elder who never had children, they would be liable; it is, therefore, written here "congregation," and elsewhere (Numbers, Ibid.) "congregation." Just as "congregation" there refers to (a beth-din where) all are fit to judge, so, "congregation" here.