The Torah states that the omer offering is sacrificed on “the day after the Sabbath.” In this context, “Sabbath” means the first festival day of Passover. Therefore, the omer must be cut and sacrificed on the sixteenth of Nisan. Because there was a sect that adopted an alternative interpretation, the Sages were insistent that the cutting of the omer take place publicly and festively.

How would they perform the rite of the omer harvesting? Emissaries of the court would emerge on the eve of the festival of Passover and fashion the stalks of barley into sheaves while the stalks were still attached to the ground, so that it would be easier to reap them. The residents of all the adjacent towns would assemble there, so that the barley for the omer offering would be harvested with great fanfare. Once it grew dark, the court emissary would say to those assembled: Did the sun set? The assembly would say: Yes. He would again ask: Did the sun set? They would say: Yes. He would then ask: Shall I reap the sheaves with this sickle? They would say in response: Yes. He would again ask: With this sickle? They would say: Yes. He would ask: Shall I place the gathered sheaves in this basket? They would say: Yes. He would again ask: In this basket? They would say: Yes. If the day for harvesting the (Mishna Menaĥot 10:3)