We inquire about and expound upon the laws of Pesaĥ beginning thirty days before Pesaĥ. We learn this from Moshe, who on Pesaĥ itself explained the matter of Pesaĥ Sheni, the make-up date for those unable to bring the Paschal offering, which takes place thirty days later. The main reason for this is that all of Israel had to prepare animal sacrifices as Pesaĥ approached, examining them to be certain that they were free of disqualifying blemishes (Pesaĥim 6a; AZ 5b).
This enactment was not canceled even after the Temple was destroyed; one must study the laws of Pesaĥ thirty days before the holiday arrives. As is well known, Pesaĥ has very many laws, pertaining to preparing the home for Pesaĥ, seeking and destroying ĥametz, baking the matza, and the Seder. Some Rishonim maintained that the enactment applies specifically to Torah scholars, enjoining them to prioritize answering practical questions about the upcoming holiday. According to this view, there is no universal obligation to set a fixed time for studying the laws of Pesaĥ (Ran and Rashba). Nevertheless, since many Rishonim maintain that it is indeed obligatory to set a fixed time for studying the laws of Pesaĥ beginning thirty days before Pesaĥ, it is proper that every individual do so, beginning on the fourteenth of Adar (Purim). It is also proper for schools and yeshivot to set a fixed time for studying the laws of Pesaĥ during this period.
There is a dispute amongst halakhic authorities on whether one is obliged to study the laws of the other holidays thirty days in advance. Some say that since this enactment was established primarily for preparing the animal sacrifices, and such sacrifices were in fact brought on the three pilgrimage festivals – the olat re’iya (pilgrimage burnt-offering), shalmei ĥagiga (pilgrimage peace offerings), and shalmei simĥa (festival peace offerings) – therefore it is proper to study the laws of each festival thirty days in advance. Others say that the practice today primarily concerns Pesaĥ, since its laws are so numerous and strict (MB 429:1).
These differences of opinion and distinctions concern advance preparations for the holidays. During the course of the holidays, however, there is an ancient enactment, ordained by Moshe, for people to study the laws and spiritual meanings of that holiday (Megilla 32a, MA 429:1).
It is also worth noting that there are authorities who maintain that the main obligation is for rabbis and Torah teachers to begin teaching the laws of Pesaĥ thirty days before the festival, but there is no obligation on each individual. This is what Ĥok Yaakov states in 429:1, 3, adding in the name of Rokei’aĥ, Raavan, and Kol Bo, that even the reading of Parshat Para right after Purim was established to remind the people to purify themselves for the upcoming Pesaĥ. Similarly, many Aĥaronim write that this is the reason for the establishment of the custom to teach the laws of Pesaĥ on Shabbat Ha-Gadol, as recorded in SAH and MB 429:2. Nevertheless, according to most authorities there is still a mitzva for every individual to delve into the laws of Pesaĥ during the thirty days prior to the festival. BHL rules accordingly. However, there is arguably a greater obligation for rabbis and teachers.