Here, the Mishnah is going to discuss what happens if the blood of a korban chatat (sin offering) gets splattered onto a person’s garment. The Mishnah says: If the blood of a korban chatat was sprayed onto a garment, the garment has to be laundered to remove the bloodstain. The Torah tells us that if a sprinkle of blood goes onto a garment, it has to be laundered in a holy place, which means in the courtyard of the Mishkan (Tabernacle), and it has to be laundered with seven different cleaning agents to remove the stain.
Even though, if you look at that pasuk (verse), it is only talking about the korban chatat that is eaten, there are two types of korban chatat. There is a korban (offering) offered on the outer Mizbeach (altar), outside the heichal (sanctuary), and its meat is eaten by the Kohanim (priests). The inner korban chatat is one where the blood is sprinkled inside the heichal; its meat is not eaten but is burned in Yerushalayim.
Even though this pasuk tells us that the clothes have to be laundered after blood is sprayed onto them, it is only talking about someone dealing with a korban chatat that is eaten, as the pasuk tells us that it should be eaten in a holy place. Even though it says that, if blood from either the korban chatat that is eaten or the korban chatat that is offered inside, which is not eaten, gets on a person’s garment, the garment has to be laundered; these are both types of korbanot (offerings). This is what is said: “This is the law for the chatat.” We learn from there, when it says that, that there is one law for all the chatat offerings, whether they are offered outside, where they are eaten, or inside, where they are not eaten. There is one law for all of them, and therefore, if blood gets on the garment, it is laundered.