Rambam - 1 Chapter a Day

I.e., the court of 71 judges described in Hilchot Sanhedrin 1:3. Since this book of the Mishneh Torah contains the laws pertaining to the establishment of the Supreme Sanhedrin, the Rambam mentions the laws governing a person who rebels against that court in the same book (Radbaz).

As the Rambam explains in his introduction to the Mishneh Torah, from the Written Law alone, it is impossible to know how to observe the mitzvot. Instead, the explanation of their particulars was conveyed by the Oral Tradition from one generation to another. In each generation, the Supreme Sanhedrin in Jerusalem was considered the repository of that tradition and given the authority to clarify any and all questions regarding Jewish observance. Moreover, using the accepted principles of Biblical exegesis, they could develop new laws and insights.

I.e., the Torah promises that there would be a High Court whose authority we are obligated to heed.

Sefer HaMitzvot (positive commandment 174) and Sefer HaChinuch (mitzvah 495) count this as one of the 613 mitzvot of the Torah.
There are commentaries who maintain that this mitzvah (and the negative commandment in the following halachah) apply only to the High Court which holds sessions in the Chamber of Hewn Stone in Jerusalem. If it holds sessions elsewhere, even when sitting with 71 judges, these mitzvot do not apply. There are, however, other authorities who differ and maintain that they apply regardless of where the court holds session. The Sefer HaChinuch, loc. cit., goes even further and maintains that these mitzvot include even the obligation to heed the directives of courts in the present era.

I.e., any believing Jew.

Sefer HaMitzvot (negative commandment 312) and Sefer HaChinuch (mitzvah 496) count this as one of the 613 mitzvot of the Torah.

On this verse, the Sifri comments: “Follow them even if they tell you that left is right.”

I.e., in the case of a rebellious elder as stated in Chapter 3. See Hilchot Sanhedrin 18:2 which states that when a prohibition involves capital punishment, lashes are never given for its violation.

E.g., the thirteen principles of Biblical exegesis stated by Rabbi Yishmael at the beginning of the Sifra (and quoted in the daily prayers) or other principles of this nature.

E.g., the prohibition against eating chicken in milk. See Chapter 2, Halachah 10.

E.g., the mitzvah of eruvin; see Hilchot Eruvin 1:2.

E.g., the recitation of Hallel on Rosh Chodesh (Hilchot Chanukah 3:7).
More particularly, in his Introduction to his Commentary on the Mishnah, the Rambam defines “decrees” as referring to practices instituted to safeguard the observance of the mitzvot, and “edicts” and “customs” as referring to practices instituted on the basis of the sages’ understanding or because of mutual consent to regulate social norms or to bring people to a more complete Torah experience.

The Ramban (Hasagot to Sefer HaMitzvot, General Principle 1) challenges the Rambam's ruling, stating that if so, anyone who violated a Rabbinic ordinance would be liable for lashing, for in effect he would be violating a Torah commandment. Similarly, the general principle - When there is doubt regarding to a question of Rabbinic Law, we follow the more lenient position, while when there is doubt with regard to a question of Scriptural Law, we follow the more severe position - would not apply. For all matters would involve Scriptural Law.
The Kiryat Sefer resolves the Rambam's ruling explaining that at the outset, the Sages established their ordinances with these leniencies in mind.
In Yayn Malchut, the Lubavitcher Rebbe explains the difference between the Scriptural commandments and the obligation to heed the rulings of the Rabbis as follows: Scriptural commandments can involve the cheftza (the physical substance of the article itself); the article is forbidden. Rabbinic commandments, by contrast, can involve only the gavra (the person observing the commandment); he is forbidden to perform the act (Tzafnat Paneach, Responsum 33). Hence since with regard to a Scriptural Commandment, the object itself becomes forbidden, we rule more stringently. With regards to a Rabbinic commandment, by contrast, since the object itself is not involved, there is room for leniency.

Extending back to Moses at Sinai.

Note the Rambam’s Introduction to his Commentary on the Mishnah, where he elaborates on this subject explaining that there was never any difference of opinion among the Jewish people about which species to use on Sukkos. Although the descriptions of some of the four species in the Torah do not give clear indications which species to use, the Jewish people have always employed the same four. Similarly, in all courts throughout our people’s history, “An eye for an eye” (Exodus 21:24), has always been interpreted as referring to financial payment, not actually gouging a person’s eye out. These and other similar matters have always been universally accepted.

I.e., points derived through the accepted principles of Biblical exegesis.

As stated in Hilchot Sanhedrin 1:3-4, a court of 23 judges should be established for every city with at least 120 inhabitants. If there are less, a court of three judges is established.

See Hilchot Sanhedrin 1:3 with regard to the description of the courts mentioned in this and the following clause.

I.e., the questioner, the judges of his local court, and the judges of the court on the Temple Mount.

I.e., within the Women’s Courtyard, before the Nikanor Gates that lead to the Temple Courtyard.

See Sanhedrin 88b which states: “When the students of the Schools of Shammai and Hillel who had not studied under their masters sufficiently multiplied, differences of opinion increased among the Jewish people and it became as if there were two Torahs.” See also the discussion of the matter in the Rambam’s Introduction to His Commentary on the Mishnah.

I.e., the Supreme Sanhedrin had not reached a decision, and an action had to be taken immediately (see Lechem Mishneh).
Our translation follows the version in the standard printed texts of the Mishneh Torah. According to certain authoritative manuscripts and early printings, the version is “or the matter did not reach them,” i.e., the decision had to be made before the matter could be taken to the High Court.

From the Rambam's wording, one might think that if a later court comes to a decision based on their appreciation of the subject, the principles mentioned below are followed despite the fact that a previous court had ruled differently. Even if the former court was greater in wisdom and in the number of adherents (see Chapter 2, Halachot 1-2), the latter court's decision may be followed, as stated by Rabbi Yehoshua ben Korcha in Avodah Zarah 7a (see Kessef Mishneh).
Rav Moshe HaCohen and the Lechem Mishneh differ and cite a responsum of the Rashba (Vol. 1, Responsum 253) which states that the ruling depends on which court is greater in wisdom and in the number of adherents. The Rashba does state there is room for leniency if the matter involves a major loss. This view is cited by the Ramah (Choshen Mishpat 25:2).