The Torah introduces the complex details and laws of tzara’at, which refers to afflictions that might strike the body, clothing or one’s house. It is a source of tum’ah (a hard word to translate as well; the best we might say is “spiritual defilement determined by physical conditions”), and requires purification (taharah). Only certain types of tzara’at are rendered tamei.

And Hashem spoke to Moshe and to Aharon, saying: A person that (KI) on the skin of his flesh there shall be (YIHEYEH) a rising, an outgrowth or a bright spot, and on the skin of his flesh it shall become a plague of tzara’at; then he shall be brought to Aharon the Kohen, or to one of his sons the Kohanim (Vayikra 13:1-2).

If declared tamei, the metzora becomes a primary source. This means that he renders people tamei through direct or indirect contact, all utensils through direct contact, and the contents of a house through entry (Rambam, “ Laws of Tara’at Uncleanness” 10:11-12).

The Sages (see Torat Kohanim here, par. 36 and Horayot 10a) are puzzled by the wording of this introduction to the subject of tzara’at. The word YIHEYEH (shall be) seems to emphasize the future, suggesting that tzara’at has never occurred earlier, yet the “disease” of tzara’at did strike before: did not Hashem make Moshe’s hand turn “like snow” with tzara’at (Shemot 4:6) at the burning bush? Alternately, can we say that YIHEYEH means that only Israel will be stricken with tzara’at? This cannot be, because non-Israelites can also be afflicted with it― Na’aman, the general of Aram for example, was a metzora (Melachim II 5:1).

Malbim (R. Meir Leib ben Yechiel Michael, 1809-1877) takes further note of the word KI, meaning “that,” rather than the more common word ASHER. Torah Temimah (R. Baruch ben Yechiel Michel HaLevi Epstein, 1860-1942) combines these observations: Had the Torah wished to describe a person “in whom” there is a plague of tzara’at, it should have said ASHER BO; the phrase KI YIHEYEH – “that there will be” – seems awkward. Consequently, the unusual wording of this verse restricts the application of tzara’at, as the Sages say:
Shall be (YIHEYEH) -- From the “utterance” and on (Horayot 10a; Torat Kohanim).
Only those “plagues” that occur after the “utterance” can be proclaimed tzara’at, and thus tamei.

When was the “utterance”?

Most commentaries identify the “utterance” with the Revelation at Sinai (Rashi; R. Ovadia of Bertinoro, c. 1450-c. 1515; see also Avoda Zara 5a, Tosafot s. v. Ela; Nedarim 7b; Rabbenu Asher ben Yechiel, c. 1250-1327 and Rabbenu Nissim ben Reuven Gerondi, c. 1310-c. 1375).

Torah Temimah however, disagrees, since the Sages teach that all afflicted Israelites were cured at Sinai (Bamidbar Rabbah 7:1; Shir HaShirim Rabbah 4:7)! And, even according to the view that they returned to their afflicted state after the sin of the golden calf (ibid.), all plagues would have occurred “after the utterance.” Thus, Torah Temimah insists that the “utterance” was not the Revelation of the Decalogue per se, but rather the
moment the laws of tzara’at were first taught (compare Nazir 54a, Tosafot, s. v. O kever; and Yevamot 61a).

The Torah therefore means to say:
A person that (KI)[from this moment on] shall be (YIHEYEH) on the skin of his flesh …
However, “plagues” of tzara’at that existed before the giving of the Torah cannot be declared tamei.

Malbim argues that the use of KI, rather than ASHER, is also relevant. In accordance with Malbim’s principles of interpretation, ASHER would have even included a pre-existing condition, while KI is restricted to a new condition.

It is thus established that only a plague that appears after the “utterance” can be declared tamei, whereas a plague existing from before can never become tamei. (The principle of “from the utterance on” is also found in other areas of Halacha, but this is not the place to elaborate.)

The principle of “from the utterance and on” is further extended to other cases of tzara’at, such that any plague that appears under conditions of exemption is clean, even if the plague remains after the conditions of exemption have expired. Other examples of exempted individuals are Gentiles and a fetus in utero (Mishnah Nega’im 3:1; Arachin 9a; Rambam, “Laws of Tzara’at Uncleanness,” 9:1).

Consequently, the Mishnah (Nega’im 7:1)
formulates the law as follows:
These “bright spots” are clean: Those from before the giving of the Torah, on a Gentile who converted, on an infant born with it …
Rambam rules accordingly (“Laws of Tzara’at Uncleanness,” 6:4), although he does not mention the case of a plague that existed before the giving of the Torah.

What is the implication of the principle of “from the utterance and on”?

In the physical world, objects cast shadows. The perception of a shadow is evidence of the existence of an object. Furthermore, the larger the object, the larger is the shadow it throws.

We might use the analogy of objects and their shadows to understand, at some level, tumah and kedushah (sanctity): The possibility of tum’ah is a reflection of sanctity. What is more, the greater the sanctity, the more are the possibilities for tum’ah.

Thus we see how the giving of the Torah, which
creates the sanctity of the Jewish people, also creates the concomitant possibility of tumat tzara’at. Of course there was the plague of tzara’at before the Torah was given, and of course the plague of tzara’at occurs to others outside the people of Israel. But there is no tumat tzara’at without kedushat Yisrael.

We are who we are – the sanctified people of Israel – thanks to the Revelation and teaching of Hashem’s Torah.