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1. Learning the laws prior to the festival:
It is a Mitzvah upon every Jew to study the laws of Pesach prior to the festival until he is an expert in them, and knows what is to be done. One is to study the laws from books dealing with the practical laws of Pesach, or alternatively, is to learn the laws from a teacher.
From when before Pesach is one to begin studying the laws? One is to begin studying the laws thirty days prior to the festival. Practically, one is to begin studying the laws of Pesach starting from Purim [which is the 14th of Adar]. [One is to begin learning the laws on Purim itself.]
Increasing in study two weeks prior to Pesach: One should increase in learning these laws from two weeks before Pesach, thus following the opinion of Rav Shimon Ben Gamliel.
Starting from Purim, the 14th of Adar, it is a Mitzvah upon every individual to study the laws of Pesach, until he is expert in them.
Studying Miseches Pesachim:
It is proper to study the Talmudic Tractate relevant to the festival, prior to each festival. Thus, prior to Pesach, one is to study Miseches Pesachim.
Not to eat Matzah:
The Chabad custom is not to eat Matzah starting thirty days before Pesach, which is from Purim and onwards. [Others have the custom to avoid eating Matzah starting from Rosh Chodesh Nissan. Others avoid eating it starting from the night of the 14th. According to all it is forbidden to eat Matzah starting from the day of the 14th, which is Erev Pesach.]
 Admur 429:1-3; Hisvadyos 1982 Vol. 4 p. 2154
Background of this ruling from Admur 429:1-3:
The early Sages, in the times that the Temple was established, instituted that the preachers should begin to teach publicly the laws of the upcoming festival thirty days prior to the festival. Thus, from Purim and on they would expound on the laws of Pesach. From the fifth of Iyar and on they would expound on the laws of Atzeres [Shavuos], and from the 14th of Elul and on they would expound on the laws of the Chag [Sukkos].
The reason behind this institution: Every Jew living in Eretz Yisrael during the times of the Temple, was obligated to bring three sacrifices [to the Temple] on the Festival [the Olas Riiyah, Shalmeiy Simcha, and Shalmeiy Chagigah]. Now, being that the animals to be sacrificed must be clean of blemishes and other invalidations, therefore the Sages instituted for the preachers to begin expounding on these laws thirty days prior to the holiday, in order to remind the people of the festival, so they do not forget to prepare animals which are kosher for the sacrifice. They thus had thirty days for preparation. [429:1]
Does this institution apply even today? Even after the destruction of the Temple this institution remained active, as every Rebbe would teach his students the laws of the upcoming festival thirty days prior, in order so they become experts in the laws of the festival, and know that which has to be done. [429:2] In today’s generations however since the Rabbi’s no longer teach the laws to the students (being that they are already all written in books), it is therefore a Mitzvah on every person to learn the laws of the festival prior to the festival until he is expert in them, and knows what is to be done. [429:3]
 What is the meaning of the term “Mitzvah”; is it obligatory, or voluntary? Some write that the term Mitzvah is not a complete obligation. [Chazon Ovadia Pesach p. 1; See also Kelalei Haposkim page 187 that the term Mitzvah is not an obligation.] Possibly, one can explain that today it is not an absolute obligation since everything today is written in Sefarim, and one can simply look up a Halacha when it comes up, and thus there is no obligation to actually learn all the laws prior to Pesach. Alternatively, one can explain that the institution of the Sages was only for the teachers and not the students, thus one cannot consider it an obligation for the student to learn. [See previous footnote]
 Admur ibid; M”A 429:1; Majority of Poskim and Rishonim brought in Biur Halacha 429:1 “Shoalin”
Other Opinions-Asking the laws? Some Poskim write that “One asks about the laws of Pesach thirty days before” and not that “one expounds the laws of Pesach thirty days before.” [Michaber 429:1; Tur 429; Rif; Wording in Pesachim 6a and Bechoros 58] This can possibly be interpreted to mean that the Mitzvah is not to teach the laws but rather that if two people ask a question to a Rabbi, then the one who asks regarding Pesach receives precedence. And so is the ruling of the Ran Perek Kama Pesachim and Rashba Perek Daled Megillah that there is no Mitzvah to teach the laws, and rather the Mitzvah is simply to give precedence to questions. Admur ibid, based on the Magen Avraham ibid, is thus negating this opinion in their wording. Furthermore, see Biur Halacha ibid who learns that majority of Poskim and Rishonim rule that one must teach the laws and that is the intent behind the word Shoalin in the Gemara ibid and used by the Michaber ibid. There is thus no dispute between the Michaber ibid and Admur in this matter, and the opinion of the Rashba and Ran are negated in face of all the other Poskim.
 Admur 429:1
 Ateres Zikeinim 429; M”B 429:2; Hisvadyos 1982 Vol. 4 p. 2154 mentions to begin learning the laws of Sukkos from the 14th of Elul
Ruling of Admur in 429:3: Admur ibid mentions studying the laws thirty days before hand only with regards to the preachers, as was done in the times of the Temple. However, regarding today’s times that all the laws are written in Sefarim, he does not write how many days before hand one is to begin the study. However, in Ateres Zikeinim 429, he writes that even in today’s times that all the laws are written in books, one is to study the laws 30 days before.
 Chok Yaakov 429:4; Yad Ahron on Beis Yosef; Mishneh Berurah 429:2 in name of above Poskim and Gr”a; See Toras Menachem 1984 2:1349
The calculation: Nissan includes 14 days of learning until Pesach which is on the 15th. Thus, one needs to learn an additional 16 days in Adar to make up the 30-day period prior to the festival. Now, since Adar is always a 29-day month, even in a leap year, therefore one must begin from the 14th, for a total of 30 days.
Other opinions: See Chikreiy Halachos 1:22 of Rav Pekarsky who learns in Admur that the 30 days begin from after Purim. See Bach 429
 Talk of Rebbe, brought in Hamaaseh Hu Haikur; See Pesachim 6a
 Shelah Hakadosh, brought in Piskeiy Teshuvos 429:1
 Igros Kodesh 8/319; See Igros Moshe 1/155
The reason: Although from the letter of the law it is permitted to eat Matzah prior to Erev Pesach [471/4] nevertheless some are accustomed to avoid eating Matzah thirty days before hand, as the entire reason behind not eating Matzah is so one does not experience the Mitzvah prior to its proper time, just like one may not have relations with an Arusa until Nessuin takes place. Accordingly, it is proper to avoid eating Matzah starting thirty days beforehand, as is the ruling with all matters relating to Chameitz. Nevertheless the Sages did not desire to establish such a decree due to difficulty for it to be upheld by the public. It was therefore only prohibited on Erev Pesach. [Igros Moshe ibid] Alternatively the reason is in order so the Matzah be new and beloved onto the person. [Likkutei Mahrich Seder Hanhagas Chodesh Nissan p. 3b]
 Shvus Yaakov 471/7 based on Shiyurei Kneses Hagedola 471/3; Beir Heiytiv 471/5; M”B 471/12; Igros Moshe 1/155 writes that many are accustomed like this ruling. Lev Chaim 2/88 writes it is a mere stringency and is not required from the letter of the law.
The reason: They follow the same reasoning explained in the previous custom of avoiding Matzah for thirty days. Nevertheless they only avoid from Rosh Chodesh, as according to Rav Shimon Ben Gamliel the Chameitz laws relevant to Pesach only being to apply two weeks before hand and not from thirty days. [Igros Moshe ibid]
Other Opinions: Some Poskim ridicule the custom to avoid eating Matzah before Erev Pesach. [Orchos Chaim Spinka in name of Meoreiy Oar “Oad Lamoed” p. 35b] There he writes that one should not say that many [Rabim] are accustomed to avoid Matzah starting from Rosh Chodesh, rather one should read Rakim [ignoramuses] are accustomed as they are arguing on the decree of the Sages which only begins to apply on Erev Pesach.
 M”A 471/6 in name of Ran; So rules Igros Moshe 1/155; Rav Poalim 3/27