Chapter 6, Mishna 1
The Paschal lamb offering, like the daily offering in the Temple, overrides Shabbos (when it is normally prohibited to slaughter animals). These offerings may not be brought by someone who is tamei, ritually impure, UNLESS the majority of the nation is tamei. There are may different sources of tumah, and they each have their own rules, such that it is difficult to say that one kind of tumah is “worse” or “stronger” than another. The three “camps” in the wilderness – the Tabernacle, Camp of the Levites, and Camp of the Israelites – have analogues centuries later in the Temple, Temple Mount and Jerusalem/Walled Cities of Israel.