וּכְלִי־חֶרֶשׂ אֲשֶׁר תְּבֻשַּׁל־בּוֹ יִשָּׁבֵר וְאִם־בִּכְלִי נְחשֶׁת בֻּשָּׁלָה וּמֹרַק וְשֻׁטַּף בַּמָּֽיִם
An earthenware vessel in which it is cooked shall be broken, but if it is cooked in a copper vessel, it shall be purged and rinsed with water.
It is not coincidental that the festival of Pesach always follows the reading of Parashas Tzav. The reading of specific Torah portions in connection with specific holidays dates back to Moshe Rabbeinu (Megillah 31b). Tzav is read before Pesach, Bamidbar before Shavuos, Va’eshanan after Tisha be’Av and Nitzavim before Rosh Hashanah.
There are two reasons for the reading of Parashas Tzav before Pesach. The first and most important explanation relates to the concept of biur chametz – cleansing one’s home and utensils of leaven. The Torah mentions this act twice: in Parashas Tzav and later in Parashas Matos. Parashas Tzav, which sets forth the laws of kashering metal utensils that have absorbed the taste of a sacrifice, contains the basic halachos. The kashering of utensils for Pesach are derived from the rules of merikah and shetifah, purging and rinsing, mentioned in this verse.
In the Beis Hamikdash, the meat of a sin-offering must be eaten within a single day and night after the sacrifice. The cooked meat of a korban shelamim must be eaten within two days and one night (7:16). After this time, the meat becomes nosar, which is forbidden to eat. Therefore, the taste of the sacrifice absorbed in the pot must be removed by means of hagalah – immersion in boiling water.
In the Mishneh Torah, the Rambam distinguishes between an ordinary utensil that became forbidden to use by absorbing the taste of a forbidden food, and a utensil intended for use on Passover. An ordinary non-kosher utensil requires only hagalah, placing the item in boiling water (which according to Rashi in Zevachim 97a is the same as merikah) to once again become permissible to use (Hilchos Ma’achalos Assuros 17:4). However, when one cleanses a Passover utensil, hagalah alone is not enough. The vessel must also be rinsed in cold water (Hilchos Chametz Umatza 5:23). This process, which is called shetifah, is derived from this verse.
Tosafos, on the other hand, maintains that shetifah is not necessary to render utensils kosher for Passover. Tosafos (Zevachim 96b, d”h lo tzericha) contends that merikah and shetifah are required only in the Beis Hamikdash. Since vessels which have absorbed kodshim (sanctified ingredients) must not be removed from the Temple court, the procedure of merikah and shetifah was introduced so as to allow such removal: וּמֹרַק וְשֻׁטַּף.
Tosafos’ opinion is based on the assumption that it is insufficient to merely eliminate the sanctified foodstuff from the vessel via hagalah, but that an additional procedure was necessary, even though such a procedure does not play any role in removal of the absorbed sanctified material. Conceptually, according to Tosafos, there are two steps to allow a Temple vessel to be used outside the Temple: removing the absorbed sanctified foodstuff via hagalah, followed by another procedure, shetifah, which provides license (that is, acts as a matir) to allow the transfer from a sanctified to a non-sanctified domain.
The Rambam indicates that this same double procedure used in the Temple is required to kasher vessels for Passover as well. Utensils that are used for Passover require an additional procedure beyond hagalah. There is a special rabbinic prohibition against using chametz vessels on Pesach even if the absorbed chametz would be entirely removed via hagalah. Performing shetifah provides the dispensation or matir that allows us to use chametz utensils during Passover, after the absorbed chametz is removed..
The merikah and shetifah procedure discussed in this parashah is not limited to sanctified vessels of the Temple, but also provides the model allowing the use of non-Pesach utensils on Pesach. This is one reason why Parashas Tzav is read the week before Pesach. (Darosh Darash Yosef pp. 214-216, Gan Shoshanim, Vol. 1, p. 33, Harerei Kedem, pp. 78-82)