It is a positive Torah precept to remove chametz before the time that one is forbidden to eat it. The verse states: But by the first day all chametz shall have been removed from your home. According to tradition, the first day refers to the fourteenth of Nissan.
Proof for this can be drawn from the verse which states: You shall not sacrifice the Paschal offering while there is still chametz (ibid. 23:18), for since we know that the Passover sacrifice was offered on the fourteenth of Nissan, we can deduce that the obligation to remove chametz must also be on the fourteenth of Nissan.
To what does the Torah refer when it speaks of removing chametz?
The reference is to nullifying it in one's mind, to considering it as dust, and as being no longer in his possession. One must consciously consider all of the chametz that is in one's possession as if it were as useless and worthless as dust.
The Rabbis ordained that removing one's chametz also includes searching in every corner of one's home to ensure that all of one's chametz has been removed. Moreover, they decreed that this search should be made on the eve of the fourteenth of Nissan by the light of a candle. It is customary not to schedule periods of Torah study on the eve of the fourteenth, for one might become involved in study and delay the removal of chametz at the set time.
By nullifying one's chametz in one's mind and considering it as being no more than dust, and thus ownerless, one fulfills the mitzvah of removing chametz from one's possession. By doing so, one can prevent himself from being guilty of transgressing the commands which forbid him from seeing and/or having chametz in his possession, for these mitzvot apply only to chametz which is his. The Sages explained that the verse which states: All chametz shall not be seen by you (ibid. 13:7), means that one is forbidden to see chametz which belongs to him..
The prohibition does not apply to chametz which is either ownerless or which belongs to someone else. If this is the case, why then is it necessary to conduct such a thorough search for chametz? Why not simply render it ownerless by nullifying it?
There are two reasons why we are so thorough in searching for chametz. The act of nullifying chametz and declaring it ownerless depends upon a person's thoughts.
It is only efficacious if one does so with complete sincerity and intent. Since people do not all think the same way, some may treat the matter more lightly and not renounce their ownership of the chametz with complete intent.
The Sages therefore decreed that the nullification of one's chametz must be preceded by complete removal, accomplished by searching for it throughout the house.
In this way, the person shows that he sincerely intends to render his chametz ownerless. Secondly, since a person is accustomed to eating chametz in his home all year, were he not obligated to physically remove it from his home, he might forget that there is a probibition of eating chametz on Passover.
The Sages therefore ruled that the chametz should be removed and not simply nullified and rendered ownerless.
Even though the Sages ruled that we must search for chametz and remove it from our possession, we are also obligated to renounce our ownership of it.
This must be done after the search, for it is possible that a person might not have searched properly, and a small portion of chametz might have been overlooked, in which case one would be transgressing the prohibitions of having chametz in one's possession on Passover.
Alternatively, one might have deliberately set aside a small portion of chametz for some specific reason and forgotten about its existence.
Or, one might come across chametz on Shabbat, or on the first or last day of Passover, when one would be unable to burn and destroy it. Moreover, even if one found the chametz during the intermediate days of Passover, he might delay destroying it immediately.
For every moment that he delays doing so, he is guilty of having transgressed the mitzvot of not seeing or having chametz on Passover. The Sages therefore ordained that besides searching for and removing chametz, one must also render it ownerless.
In this manner, even if he finds chametz on Passover, he will not be culpable since it is not his.
In our discussion thus far, we have established that the obligation to search for and actually remove chametz from one's possession is a Rabbinic requirement.
By Torah law, nullification alone would be sufficient. However, sometimes the nullification of one's chametz alone does not suffice to prevent one from being guilty of transgressing the Torah prohibitions of having chametz in one's possession.
If one did not declare his chametz ownerless before midday on the fourteenth of Nissan, either because of extenuating circumstances or because he forgot, a mental renunciation of ownership of the chametz will now no longer be effective, according to Torah law.
Once the period has elapsed during which a person must render his chametz ownerless, he may not derive any benefit from chametz.
The chametz is thus seen as being ownerless since he is forbidden to derive any benefit from it, and one cannot renounce or nullify something which is no longer his.
Nevertheless, though the chametz is deemed ownerless because one cannot derive benefit from it, it is not considered to be ownerless as to the prohibitions against seeing or possessing it.
Thus, even though the person cannot nullify or renounce ownership of his chametz, he is still culpable for having it in his possession. The only way in which he can prevent himself from transgressing is to physically search for and destroy the chametz.