Keilim, Chapter 24, Mishnah 1. This chapter presents a long series of mishnayot built on a single pattern: a familiar object is named, and the Mishnah tells us that there are three varieties of it, each one carrying a different status in the laws of tumah. Our mishnah opens the series with shields.
Before entering the details, it helps to have the three-way framework in mind, because it repeats itself again and again through the chapter. One and the same object can be produced for very different purposes, and its purpose determines which forms of tumah can take hold of it.
- An item fashioned so that a person will sit or lie upon it. Such an item can receive tum'at midras, the tumah transmitted by the pressure of a zav or a niddah who leans, sits or lies on it.
- An ordinary utensil that was not designed to be sat or lain upon. It is still a keli in every respect, so it can contract tumah by contact, but midras does not apply to it.
- An item that cannot become tamei at all, for one reason or another. It stands outside the system entirely.
Shelosha terisin hem
The Mishnah opens with the words "Shelosha terisin hem." A teris is a shield, and the Mishnah teaches that shields come in three distinct kinds, with each kind landing in one of the three categories outlined a moment ago.
The curved shield
"Teris hakafuf tamei midras." The curved shield is the shield of actual warfare. It is bent in such a way that it wraps around the soldier and screens him on three sides. Why should a shield be subject to midras, which belongs to objects made for sitting and lying? Because on the battlefield the soldier used it as his bed: he would stretch out and sleep on it. Since lying upon it is one of its intended uses, it is included among the items that receive tum'at midras.
The shield of the sporting arena
"Veshemesachakim bo bakunpon tamei tumei met." The second shield is flat and round, and it belongs to the arena, where in the times of the Mishnah men would fight one another as sport. This shield is a genuine keli with a genuine function, so it can contract tumah, including the tumah of a corpse. But nobody sits or lies on it; it serves purely as an implement held in the hand. Therefore midras does not apply to it, and it remains in the second category: contact tumah only.
The Arabs' play shield
"Vedishata arviyin tehorah miklum." The third is the small shield used by the Arabs in their games, and it is pure from every form of tumah. The reason is that it has no real function at all. It is not a shield in any practical sense: it would not stop a sword, and it protects no one. It exists for amusement and nothing else. A plaything is not regarded as an object with a useful purpose, and an object with no useful purpose is not a keli. Having no function, it can never become tamei.
So the three shields lay out the chapter's pattern in full: one that a person lies upon and therefore receives midras, one that is a working utensil and therefore receives corpse tumah alone, and one that is a mere toy and therefore receives nothing at all.