A new chapter - focused on the grain-offering that is the omer, brought on the 16th day of Nisan, the second day of Pesach, and which allows the "new" grain (or removes the prohibition against it. So, beginning with the new mishnah - on the case of the day of the omer offering falling on Shabbat, which is the unusual case, not the norm. The proper date of this entails a decision made against those who pushed for a different (regular) date, and therefore a good deal of ceremony to make the point. But with an effort to minimize the degree of violation of Shabbat. Also, the mitzvah of bringing the barley for the omer offering was first for the fields in proximity to Jerusalem, unless that barley didn't ripen, and then they could look farther afield. At the time of a civil war - in the Hasmonean era - during a time of siege, including an old man who knew "Greek wisdom," who fundamentally let the besiegers into the city. He acknowledged that the correct offerings were protecting those within the city of Jerusalem, and then the people outside of the city finally sent in a pig for an offering, and that was beyond bearing.