Naftali Cohn, "The Memory of the Temple and the Making of the Rabbis" (from: The Memory of the Temple and the Making of the Rabbis (University of Pennsylvania Press, 2013)

The rabbis construct the Court and its members as their predecessors in Temple times, so the past in these accounts functions as a mirror on the present, reflecting the image of the rabbis as they see themselves. And the memory of the past, in which the rabbinic predecessors are legal-ritual authorities, makes an argument for rabbinic legal-ritual authority in post-Temple times.

By inserting the Court into the past, the rabbis are asserting the antiquity of and providing a myth of origins for the role they claim for themselves within society...

Throughout the Mishnah... the court appears numerous times in an abstract sense, as a legal body that hears and adjudicates cases (or the location where this judicial institution engages in its activities), as
well as in the concrete historical sense, as a legal institution existing in the time of the Temple.

When referring to the purportedly historical Court of the Second Temple era, the Mishnah uses a number of different terms: בית דין (bēit din, Court), בית דין הגדול שבירושלים (bēit din haggadōl shebiye˘rushālayim, the Great Court in Jerusalem), and סנהדרין/סנהדרים (sanhedrin/sanhedrim =
synedrion [council, court]). Members of this court are called זקן or זקנים (zākēn or z˘ekēnim, elder or elders). In the Mishnah’s narratives about events from Temple times—and, to an extent, throughout the Mishnah—the terms are essentially interchangeable, and each of these terms seems to refer to the institution of a central, authoritative court and its members...

The elders and the Court who play such an important role in Temple ritual narratives do appear in earlier Jewish literature. The Hebrew Bible and the Septuagint frequently mention elders ( זקנים [ze˘kēnim] in hebrew; presbyteroi, in Greek). In the Septuagint, the term gerousia, council, is frequently used where
the Hebrew reads “elders,” suggesting a relationship between the two.

Postbiblical texts, especially the works of Josephus and the Gospels and Acts, refer to both elders and councils, namely local political, legislative, or judicial bodies in Judaea in late Second Temple times, which are called synedrion, gerousia, boulē, or other Greek terms. These earlier references to councils include the infamous synedrion (council) that tried and convicted Jesus. Traditional scholarship
has generally assumed that the Mishnah’s Court and these councils are identical for a number of reasons. first, the Mishnah uses the Greek term sanhedrin to refer to the Court in a few instances. Similarly, both the Court and the councils appear to have some power to mete out capital punishment. And each institution appears to have a central role in Judaean society. If we assume that the institution of the Court is the same as those appearing in earlier literature, or, more likely,

that the rabbinic Great Court/Sanhedrin of the Mishnah is based (loosely) on the institution of the local council that existed in the past and is mentioned in earlier, pre-rabbinic, literature, we can compare the
Mishnah and the earlier sources. Such a comparison reveals unequivocally that the Mishnah is unique in giving the Court (or similar institution) a role in and authority over Temple ritual.

According to the pre-rabbinic sources, the earlier institutions were not involved in, and did not have authority over, ritual in the Temple...

[T]he rabbis picture themselves as legal authorities, jurists of traditional Judaean law, who have the
power to determine how Judaeans practice traditional rituals and other cultural practices. Because they claim for themselves a legal role that provides authority over ritual practice, the rabbis imagine the ritual of the past to be controlled by a similar legal institution, and they invent a connection or possibly
emphasize an existing connection to this past institution. perhaps drawing loosely on earlier traditions about a council made up of elders, the rabbis create a past that mirrors the present as they would like it to be. They turn this council into a legal body, a Court, to which they give control over the most important
rituals of the Temple era. The Court’s invented hybrid legal-ritual role reflects the hybrid legal-ritual role that the rabbis claim for themselves. Because they see the Court as their predecessors, their memory of an authoritative Court provides a historical foundation out of which the rabbis and their role emerge.
The memory of the Temple expressed in ritual narratives thus creates a myth of origins for the rabbinic group and their legal-ritual role that makes a powerful claim for rabbinic authority in this role.
In narrating and recalling past Temple ritual, the rabbis are therefore creating a past for themselves that authorizes their own real or desired role—a role, they believe, that has always been central and has upheld tradition and correct ritual practice. The rabbinic memory of the past provides the rabbinic role with antiquity and establishes that those who have filled this role have always had authority. In the rabbinic view evidenced by the Mishnah, ritual law and practice in post-Temple times must follow rabbinic rulings just as ritual law and practice followed the dictates of their predecessors in the times of the
Temple.