Kelim, Chapter Twenty, Mishnah One
1) Pillows, bed coverings, sacks and packing cases that were damaged are still susceptible to midras uncleanness.
2) A fodder-bag that can hold four kav, a shepherd’s bag that can hold five kav, a traveling bag that can hold a se’ah, a skin that can hold seven kav, Rabbi Judah adds: also a spice-bag, and a food wallet that can hold the smallest quantity are susceptible to midras uncleanness.
3) If any of them was damaged it becomes clean, since if the primary function ceases the secondary function also ceases.
Section one: All of these items were originally made for two purposesto contain something within, and to lie or sit upon. Pillows and bed coverings contain feathers, but they are mostly made for lying or sitting upon. Therefore, they are susceptible to midras impurity (impurity conveyed by sitting, lying or leaning). Sacks and packing cases are mostly for containing things, but from the outset they also are intended to serve as seats or ground coverings. Therefore, even if they are damaged and cannot be used to hold the things that they originally held, they are still susceptible to midras impurity.
Section two: The mishnah now lists a number of types of bags, and provides a minimum amount that each must hold in order for it to be susceptible to impurity. If it cannot hold this amount, it is not useful and therefore is clean. In addition, since these things can also be used as a seat, they are also susceptible to midras impurity.
Section three: In contrast with the bags listed in section one, these bags have a main purposeto carry things inside them. Sitting is only a secondary function. Therefore, if they are damaged and can no longer carry things, they are no longer susceptible to impurity.