The role of the kohanim is to connect Israel with God, and safeguarding purity is one of the conditions that enables them to fulfill that role. Therefore, only a kohen who is ritually pure may eat teruma. For this reason, kohanim and their families must be careful not to become impure and must also protect their clothing and utensils from impurity. The laws of purity and impurity are numerous and highly complex; we will mention only a few.
In general, impurity is associated with death. A corpse is therefore the highest source of impurity, an avi avot ha-tum’a. A Jew or utensil that touches a corpse or remains together with it in an ohel – that is, under the same roof – becomes a primary source of impurity, an av ha-tum’a. A Jew who becomes impure through contact with a corpse can become pure only through a seven-day process: water mixed with the ashes of the red heifer is sprinkled on him on the third and seventh days, and on the seventh day he immerses in a mikveh. A lower level of impurity applies to a zav and a nidda. In these cases as well, impurity emerges from something that was connected to the potential for life but died, and they are therefore considered avot ha-tum’a. A zav, zava, and nidda become pure by counting seven days and immersing in a mikveh, without the sprinkling of the red-heifer waters.
A person or utensil that touches an av ha-tum’a – such as a zav, a nidda, or a person who became impure through contact with a corpse – becomes impure. After immersion, once the day ends, he or it becomes pure. A neveila or dead sheretz is also impure at the level of an av ha-tum’a. A person or utensil that touches one of them becomes impure and becomes pure through immersion and nightfall. Utensils made of stone or earth do not contract impurity.
The produce separated as teruma must also be protected from impurity. If, after being picked, the produce becomes wet with one of the seven liquids – water, wine, honey, olive oil, milk, dew, or blood – it becomes susceptible to impurity. Once that happens, if an impure person or utensil touches it, even after it has dried, the produce becomes impure. However, if it never became wet, then it was never made susceptible to impurity, and even contact with an impure person or utensil does not render it impure.
Even though teruma is specifically meant to be eaten by kohanim in purity, the obligation to separate teruma applies even when the produce has become impure. As it says: “Behold, I have given you charge of My terumot” (Bamidbar 18:8), which the Sages interpret to mean: whether the teruma is pure or impure. When the teruma is pure, it is designated for eating. When it is impure, it must be burned. However, since one may benefit from it while it burns, it is preferable that the kohen receive that benefit: if it is fruit, he may use it to fuel an oven; if it is oil, he may use it to light lamps (Shabbat 25a; MT, Laws of Terumot 2:14–15).
