An entire division of the Mishanh – Nega’im – is devoted to the explication of the laws of infectious diseases as described in the Torah. The Book of Leviticus lists the kinds of diseases that afflict the human body as well as the kind of infections that may erupt within the walls of a house.
The Mishnah (Nega’im 12:5) is especially intrigued by a particular verse that deals with the detection of a plague in a house. According to the Torah (Leviticus 14:35), the owner of the house in which such an infection is observed is directed to appear before a kohen (priest) and report that: “something like a plague has appeared upon my house.” The Mishnah wonders about the apparent doubt. Surely if sufficient evidence of a disease erupted in the house so that an owner would appear before the kohen the owner should exclaim: “A plague has infected my house!” Why does the Torah have the owner say “something like a plague?” The Mishnah concludes that only the kohen has the authority to declare the house unclean. A homeowner, even if he is a great scholar, does not have that authority. Hence, the homeowner can only say “something like a plague.”
Rabbi Israel Lifschitz, known by the name of his commentary, the Tifferet Israel, understands this mishnah as a statement of respect for the office of kohen. Similarly, the author of the Torah Temimah, Rabbi Barukh Epstein, understands this Mishnah as a precaution against appearing to render a legal decision in the presence of a kohen.
To Rabbi Eliezer bar Samuel of Metz, however, there is a more important lesson to be learned. Citing his own teachers, Rabbi Eliezer ascribes to this Mishnah the requirement that every person “train his tongue to say ‘I don’t know.”
In other words, a person should never be too sure about what he or she sees or about what he or she knows. Certainty is luxury that few of us can afford. At best, people can affirm the likelihood that a condition obtains, but absolute certainty is denied us. The wise person accepts this truth. And the Torah urges us to be wise.