Mishna - "On the night of the 14th, we search for hametz." Rashi explains the reason is so that one does not transgress the Torah prohibitions of seeing and finding hametz. This leads to a difficulty raised by Rav Yitzchak the Elder - Since the Talmud (Pesachim 6B) states, "One who searches for hametz needs to annul it," and from the Torah annulment is sufficient to avoid transgression, why did the Chachamim require searching at all? Rav Yitzchak the Elder explains that even though annulment is sufficient, the Rabbis were stringent and required searching and destroying the hametz to prevent someone from eating it. This is supported by Rava's statement (Pesachim 10), "Or perhaps it might fall and one will come to eat it." Why were the Chachamim more stringent here than with other prohibited items that don't require burning? It is because hametz is permitted year-round and only forbidden on Pesach, so people are not accustomed to separating from it. This is unlike Basar Bechalav, Orlah, and Kilayim, which are permanently forbidden. While wine is only temporarily forbidden to a Nazir, others are permitted to drink it. Alternatively, Hametz is different because the Torah is particularly strict about it, adding the prohibitions of seeing and finding. Therefore, the Chachamim required searching and burning even if one has already annulled their hametz, lest they come to eat it. The Rashba notes that according to this reasoning, the Chachamim were stringent even regarding hametz Noksheh and Ta'aroves Hametz, even though the prohibitions of seeing and finding don't apply to them. This is supported by Rabeinu Tam (Pesachim 32) who interprets "Siu'r Yisaref" as referring to Hametz Noksheh, implying a prohibition against retaining it. Otherwise, why burn it? One could keep it until after Pesach and eat it, even according to Rabbi Yehuda who only forbids actual hametz after Pesach. Since there is only one verse regarding Hametz Nokshah, even Rabbi Yehuda would concede that it is permitted after Pesach.

Tosafot questions the Gemara's phrasing: "At first glance, it could enter your mind to suggest that the one who said 'light' means that one searches for leaven by the actual light of day... and the one who said 'evening' is referring to the actual evening of the fourteenth." Tosafot clarifies that the Gemara only needs to refute the opinion of "light" meaning actual daylight. The Gemara only uses the phrase "it could enter your mind to suggest" because the opinion of Rav Huna, who interprets "Or" as "Naghei" (light), doesn't actually hold that position. The Gemara mentions the seemingly obvious interpretation of "Leilei" as literal evening only to parallel its refutation of interpreting "Naghei" literally. Therefore, concludes Tosafot, there is no need to emend the text and remove the seemingly redundant phrase, "and the one who said evening is referring to the actual evening of the fourteenth."

"And in accordance with that which Rav Yehuda said" - This is not referring to why the Gemara answers, "as the one who said, 'The morning lightened.'" Rather, it is a standalone point explaining what the verse teaches us according to everyone.

"Enter with 'it is good'" - The Ri explained that in another place (Bava Kama 60a) it seems the reason [for entering and leaving with "it is good"] is because of harmful spirits. He derives this from the verse "Do not go out, any man, from the entrance of his house until morning" (Exodus 12:22). He explains the verse as a warning against harmful spirits. This is based on the principle that "Once permission is given to the destroyer [to harm], he makes no distinction between the righteous and the wicked." According to this, one must be careful to leave [one's home] in good time even in one's own city! Why then does the Gemara mention entering first? It is the way of the Gemara to mention things in this manner. For example, regarding climbing into and out of a well in Eruvin (21a), it states "He climbs up and climbs down", even though obviously one must climb in first. Similarly, in Shabbat (34b) it says, “Twilight is like the blink of an eye: This one [the sun] enters, and that one [the stars] exits,” even though the sun sets before the stars emerge. This is difficult, because Rav Yehuda himself derives this very same law from a different verse, "Do not go out," in Bava Kama (60a). The Rashba explains that we need two verses: "The morning was light" (Genesis 44:3) teaches us that the law applies when traveling to another city even where there is no concern of harmful spirits, like with Joseph's brothers who were eleven people. The concern in such a case is falling into ditches. The verse "Do not go out," on the other hand, is needed to teach us the law applies even in one's own city, and the reason there is because of harmful spirits.