The Gemara explains that this halakha is derived from the fact that Moses was standing at the time of the first Pesaḥ, on the fourteenth of Nisan, and warning the people about the halakhot of the second Pesaḥ, which occurred a month later, on the fourteenth of Iyyar. As it is stated that God said to Moses: “Let the children of Israel perform the Pesaḥ at its appointed time” (Numbers 9:2). A subsequent verse says: “And Moses told the children of Israel to perform the Pesaḥ, and they performed the Pesaḥ in the first month on the fourteenth of the month in the evening, in the desert of Sinai” (Numbers 9:4–5). And it is written in the next verse: “And there were people who were impure due to a dead body and could not perform the Passover on that day, and they came before Moses and before Aaron on that day” (Numbers 9:6), at which point Moses explained the halakhot of the second Pesaḥ to them. This proves that one begins studying the halakhot of the Festival thirty days beforehand.

And Rabban Shimon ben Gamliel could have said to you in rejecting that proof: Since Moses was speaking with regard to the laws of Passover, he completed teaching all the matters of Passover, including those of the second Pesaḥ. Consequently, one cannot derive a principle from this case.

The Gemara asks: What is the reason for Rabban Shimon ben Gamliel’s ruling? He explains that Moses was standing on the first day of Nisan and warning about the performance of the first Pesaḥ, as it is stated: “This month shall be for you the beginning of the months, the first of the months of the year” (Exodus 12:2). And it is written in the next verse: “Speak to the entire congregation of Israel, saying: On the tenth day of this month they shall take for them every man a lamb, according to their fathers’ houses, a lamb for each household” (Exodus 12:3). The Torah proceeds to detail the halakhot of the Paschal lamb sacrificed on the fourteenth day of that month.

The Gemara asks: Although this source does indicate that one should study the halakhot of Passover prior to the Festival, from where is it derived that he was standing and saying these matters on the day of the New Moon? Perhaps he was standing on the fourth of the month or on the fifth of the month of Nisan?

Rather, Rabba bar Shimi said in the name of Ravina: The halakha is derived from here: “And God spoke to Moses in the wilderness of Sinai, in the first month of the second year after they came out of the land of Egypt” (Numbers 9:1), and it is written: “And let the children of Israel perform the Pesaḥ at its appointed time” (Numbers 9:2). Evidently, Moses taught the halakhot of Passover two weeks prior to the Festival. The Gemara asks: Here too, from where is it derived that he was standing on the day of the New Moon? Perhaps he was standing on the fourth of the month or on the fifth of the month?

Rav Naḥman bar Yitzḥak said: The halakha is derived by means of a verbal analogy between the term wilderness written here and the term wilderness written previously. It is written here: “In the wilderness of Sinai,” and it is written there: “And God spoke to Moses in the wilderness of Sinai in the Tent of Meeting on the first of the second month” (Numbers 1:1). Just as there it occurred on the day of the New Moon, on the first of the month, so too here, with regard to Passover, it was on the day of the New Moon.

The Gemara asks: If so, let the Torah write first that which occurred in the first month and then let it write that which occurred in the second month, as the portion of the Paschal lamb preceded the beginning of the book of Numbers chronologically. Rav Menashiya bar Taḥlifa said in the name of Rav: That is to say that there is no earlier and later, i.e., there is no absolute chronological order, in the Torah, as events that occurred later in time can appear earlier in the Torah.

Rav Pappa said: This principle applies only when the Torah deals with two separate matters, but within one matter, that which is written earlier occurred earlier, and that which is written later occurred later; as, if you do not say so but you claim that there is no definite order within each matter, then the hermeneutic principle: When a generalization is followed by a detail the generalization refers only to that which is specified in the detail, is problematic. This principle is valid only if there is a definite order to the verses and words in each matter. If there is no definite order, perhaps it is actually a detail followed by a generalization, which is interpreted by means of an alternate hermeneutic principle with different results.

And furthermore, this is equally difficult with regard to the hermeneutic principle: “When a detail is followed by a generalization, the generalization becomes an addition to the detail, adding cases dissimilar to the detail. Here too, perhaps it is a generalization followed by a detail, as there is no defined order. Apparently, there must be a fixed order within a given matter.

The Gemara asks: If so, based on the above reasoning one cannot apply these principles even with regard to two matters. This statement works out well according to the opinion of the one who said: With regard to a generalization and a detail that appear in the Torah removed from one another, one cannot derive a halakha from it with the principle of a generalization and a detail. However, according to the one who said: One derives from a generalization and a detail that are removed from one another by means of said principle, what is there to say?

The Gemara answers: Even according to the one who said that one derives a halakha from a generalization and a detail that are removed from one another, this applies only with regard to one matter, i.e., verses dealing with the same issue, even if they do not appear together. However, if they address two different matters, one cannot derive a halakha from a generalization and a detail, as the Torah is not written in absolute chronological order.

Rav Yehuda said that Rav said: One who searches for leaven must render all his leaven null and void, cognitively and verbally. The Gemara asks: What is the reason for this? If you say it is due to crumbs that he failed to detect in his search, they are inherently insignificant, and null and void by definition.

And lest you say: Since they are protected on account of their very presence in his house, whose protection is important to him, they are significant and are not null and void, wasn’t it taught in the Tosefta that this is not the case? When the end of the fig season arrives, and those remaining figs on the trees are few and of inferior quality, there is room to assume that the owner has renounced his ownership over them. However, he continues to guard his field due to the grapes, which are harvested at that time. Similarly, when the end of the grape season arrives, those few remaining grapes are of inferior quality and the owner guards his field due to the cucumbers and due to the gourds, which have not yet been harvested.

When the owner is particular about the figs and the grapes respectively, it is prohibited to take them, due to the prohibition against robbery, and one with permission to eat them is obligated due to the mitzva to separate the tithe from them, as they are considered like any other fruit. When the owner is not particular about them, it is permitted to eat them due to the fact that the prohibition against robbery does not apply, and one who eats them is exempt due to the fact that the obligation to separate the tithe does not apply, as they are ownerless property. This indicates that if one is not particular about an object, even if it is located in property that he is guarding for another purpose, that object is not thereby rendered significant. The same reasoning applies to breadcrumbs that remain in one’s house.

Rava said: The reason for the requirement to render leaven null and void is based on a decree lest he find a fine cake [geluska] among the leaven that he did not destroy and his thoughts are upon it. Due to its significance, he will hesitate before removing it and will be in violation of the prohibition against owning leaven. The Gemara asks: And let him nullify it when he finds it.

The Gemara rejects this suggestion. Perhaps he will find it only after it is already forbidden, and at that time it is no longer in his possession and he is therefore unable to nullify leaven when it is already Passover, as Rabbi Elazar said: Two items are not in a person’s possession in terms of legal ownership, and yet the Torah rendered him responsible for them as though they were in his property. And these are they: An open pit in the public domain, for which the one who excavated it is liable to pay any damages it causes even though it does not belong to him; and leaven in one’s house from the sixth hour on the fourteenth of Nisan and onward. As this leaven has no monetary value, since it is prohibited to eat or to derive benefit from it, it is not his property, and nevertheless he violates a prohibition if it remains in his domain.

The Gemara returns to the issue of the nullification of leaven. If so, let him render the leaven null and void during the fourth hour or let him render it null and void during the fifth hour of the fourteenth of Nisan. Why is he required to do so when he searches for leaven on the evening of the fourteenth? The Gemara answers: Since the fourth hour is neither the time of the prohibition of the leaven nor the time of its removal, it is a nondescript point in time. There is concern that perhaps he will be negligent and will not render it null and void, and the leaven will remain in his possession.