Yesterday, we addressed the well-known halakha (Shulchan Arukh, O.C. 444:1) that when Erev Pesach falls on Shabbat, such that bedikat chametz cannot be performed on the night of the 14th of Nissan as usual, it is performed the previous night, on the 13th of Nissan. As we saw, this halakha could, in theory, be perceived in two different ways. One possibility is to compare this situation to one of “ha-mefaresh ve-yotzei be-shayara” – one who leaves on a trip before the night of the 14th of Nissan, and will not be home on that night, and thus performs bedikat chametz the night before he departs (Shulchan Arukh, O.C. 436:1). According to this perspective, Chazal instituted only the 14th of Nissan as the time for bedikat chametz, and in a year when this night is Shabbat, we by necessity search earlier, but this search does not fulfill the formal requirement of bedikat chametz. Alternatively, however, we might understand that Chazal from the outset instituted bedikat chametz to be performed on the night of the 14th in a regular year, and on the night of the 13th in a year when the 14th is Shabbat. According to this understanding, searching on the night of the 13th in such a year fulfills the formal obligation of bedikat chametz no less than searching on the night of the 14th in a regular year.
Seemingly, we may prove the second perspective from the fact that a berakha is recited over bedikat chametz even in a year when Erev Pesach falls on Shabbat, and the search thus takes place on the night of the 13th. In the case of “ha-mefaresh ve-yotzei be-shayara,” although some opinions (as cited in Biur Halakha, 436) require the individual to recite a berakha when he searches the night before his trip, the Rama (436:1) ruled that no berakha is recited in such a case. The Shulchan Arukh Ha-Rav explains that the traveler does not recite a berakha because he does not perform the search at the time when Chazal instituted. Accordingly, we might deduce from the fact that a berakha is recited when searching the night of the 13th when the 14th is Shabbat, that the search in such a case indeed fulfills the actual obligation of bedikat chametz, which from the outset was scheduled for the night of the 13th if the 14th falls on Shabbat. (We should emphasize that the Shulchan Arukh Ha-Rav himself rules that one recites a berakha over bedikat chametz when searching on the night of the 13th in a year when the 14th falls on Shabbat.)
It should be noted, however, that the Vilna Gaon (cited by the Mishna Berura, 436:4) offers a different reason for why (according to the Rama) the berakha is not recited in the case of one who leaves home before the night of the 14th in a regular year. The berakha recited over bedikat chametz is “al biur chametz” – making reference to the obligation to eliminate one’s chametz on the 14th of Nissan. The search for chametz is performed for the purpose of fulfilling the requirement to eliminate one’s chametz, and so the berakha is formulated in this manner, in reference to the mitzva of bi’ur – eliminating the chametz. In the case of “ha-mefaresh ve-yotzei be-shayara,” the Vilna Gaon explained, the person intends not to eliminate the chametz, but rather to remove it from the home, because he will not have the opportunity to do so later, when required. Conceivably, he might still eat or sell this chametz, as plenty of time remains before the 14th of Nissan, when eating and owning chametz becoming forbidden. Therefore, this search cannot be said to be performed as part of the bi’ur process, and thus the berakha “al bi’ur chametz” is not recited. This explanation is not applicable to the situation when Erev Pesach falls on Shabbat, because the search on the night of the 13th indeed serves the purpose of bi’ur chametz, as we eliminate the chametz the following day, on Friday (saving some chametz for Shabbat). According to the Gaon’s understanding, then, the fact that we recite the berakha over bedikat chametz in such a case does not prove that the search on the night of the 13th differs from the case of “ha-mefaresh ve-yotzei be-shayara” and fulfills the formal bedikat chametz obligation.
(Taken from Rav Raphael Binyamin Cohen’s article in Umka De-parsha, Shabbat Parashat Vayikra, 5771)