The Rabbi Is Not Enough

The opening Mishna in Sanhedrin says that three judges are required to form a Beit Din. Why are three judges required, why can't a rabbi tell the litigants the din the same way he will pasken any rule of issur veheter? The Chashek Shlomo says that three is only required to be the שוטרים to enforce the pesak. This is difficult for the Mishna is discussing how many judges are necessary to enact the law? The only reason to have three judges is to act as the policemen to ensure their pesak is carried out. Furthermore, Tosfot Sanhedrin (2b) ד”ה ליבעי is clear that the paskening the law and enforcing it are two distinct matters, not the Chashek Shlomo who lumps the two together?

The Chazon Eish says is that a Beit Din is required to create a monetary obligation. In other words, a rabbi can tell the one obligated to pay that the Torah holds him responsible but he can't create an obligation on the individual to pay. It is a Beit Din only that has the power to create a monetary obligation. What difference does it make if he is the Torah considers him obligated or this is an actual obligation upon him? The Chazon Eish says the נפקא מינה is regarding תפיסה. Only if there is a pesak of Beit Din making one obligated can the other party grab the money that is entitled to them. Without the chiuv on the obligated party, it would be theft to grab what one is owed from them.

Rav Shmuel Rozovski (Chiddushim siman 2) brings a few proofs that even when there is no monetary obligation, 3 judges are still required to form a Beit Din. One of his proofs is from the Mishna at the beginning of Maakot which assumes that it is Beit Din accepting the testimony of witnesses that a kohan is pasul. In that instance there is no monetary obligation, yet a Beit Din is still required to accept the testimony. So why is a Beit Din required?