(1) YE SHALL NOT ADD [UNTO THE WORD WHICH I COMMAND YOU] — “such as placing five sections [of the Torah] in the phylacteries, five species in a Lulav. The same principle applies to the prohibition, neither shall ye diminish from it” [by placing three sections of the Torah in the phylacteries etc.]. This is Rashi’s language. And thus the Rabbis said in the Sifre:24Sifre, R’eih 82. “Whence do we know that you are not to add to [the four species in the commandment of] the nor to the [four] fringes?23Further 22:12. Scripture therefore says, Ye shall not add. And whence do we know that you are not to diminish from them? Because Scripture states, neither shall ye diminish. Whence do we know that if [a priest] began to recite the Priestly Blessing25Numbers 6:24-26. he is not to say: ‘Since I began to bless [the people], I will [further] say, The Eternal, the G-d of your fathers, make you a thousand times so many more as ye are?’26Above, 1:11. Because Scripture states, [Ye shall not add] unto the ‘word’ — even ‘a word’ you are not to add to it.” However, not only concerning these [commandments] have the Rabbis said [that the prohibitions neither to add nor to diminish, apply], but also in the case of someone who sleeps in a Booth on the eighth Day [of the Festival of Tabernacles]27Leviticus 23:42: Ye shall dwell in Booths ‘seven’ days. Thus the Torah specifically states that the commandment to dwell in Booths applies to seven days only, and not to the eighth Day, which is a separate festival (Shemini Atzereth). Sleeping is part of the commandment “to dwell” in a Booth. [However, because of the general rule that he who feels uncomfortable is exempt from sitting in a Booth, sleeping there, in the colder climates in which we live, is practiced only by those who are very strict in religious observance (Orach Chayim 639:2, R’ma).] with the intent [of performing a religious duty] that he is liable to whipping [for having added to the commandment], as is mentioned in Tractate Rosh Hashanah.28Rosh Hashanah 28 b. So also if he were to observe the Festival of Tabernacles for only six days, he would be transgressing this negative commandment [neither shall ye diminish from it].
In my opinion, even if someone devised an independent commandment [rather than altering an existing one] such as establishing a festival in a month which he had devised of his own accord,29I Kings 12:33. as Jeroboam did,29I Kings 12:33. he transgresses the negative commandment [Ye shall not add unto the word which I command you]. And so did the Rabbis say with reference to the reading of the Scroll of Esther [on Purim]:30Megillah 14 a. “One hundred and eighty prophets31In our text of the Talmud: “Forty-eight prophets.” See my Hebrew commentary, page 360. arose in Israel and they did not diminish from nor add even one letter to what was written in the Torah, except for reading the Scroll of Esther [which was instituted by the prophets]. What basis did they have for that? etc.”32“Rabbi Chiya bar Abbin in the name of Rabbi Yehoshua ben Korcha said: It is a matter of kal vachomer (reasoning from minor to major): If [when Israel was delivered] from slavery to freedom they sang [in praise of G-d], how much more ought they to do so when they were saved from death [that was decreed upon Israel through the plot of Haman] to life!” (Megillah 14 b). The reading of the Scroll of Esther constitutes the praise to G-d for our deliverance (ibid.). And in the Yerushalmi it is stated:33Yerushalmi Megillah I, 7. On the term “Yerushalmi” see Vol. III, p. 192, Note 44. “Eighty-five elders, among them many prophets, were troubled about the matter [of the new duty to read the Scroll of Esther]. They said, ‘It is written, These are the commandments which the Eternal commanded Moses.34Leviticus 27:34. These are the commandments that [we] were ordered by the mouth of Moses, and Moses told us that no other prophet is destined to establish anything new for you — and Mordecai and Esther want to establish something new for us!’ They did not move from there while discussing the matter, until the Holy One, blessed be He, enlightened their eyes [and they found the new commandment intimated in the Torah, Prophets, and Writings].” Thus you see that [the institution of] this commandment [of reading the Scroll of Esther on Purim] would have been forbidden to them [were it not for the fact that ultimately they found it intimated in the Torah, etc.]; otherwise it would have been included in the principle, thou shalt not add thereto.35Further, 13:1. — It should be noted that at this point Ramban cites the later verse (13:1) instead of the verse here. The reason would seem to be that the verse here relates to adding to, or diminishing from, a Divine commandment, such as placing five sections of the Torah, or only three, in the phylacteries instead of the four sections ordained. The verse of 13:1, however, refers to adding a completely new commandment to the number of Taryag (613) Commandments, or of abolishing altogether one of the Divine precepts. In speaking, therefore, of the prophetic precept of reading the Scroll of Esther on Purim, Ramban thus rightly cites the verse from further on (13:1), for were it not that the prophets and Sages of that time found it intimated in the Torah, the prohibition against instituting such a new commandment would have come under the admonition, thou shalt not add thereto. However, the prohibition against adding [to the Torah] by word of a prophet we derive only from the verse stating, These are the commandments,34Leviticus 27:34. which establishes,36Torath Kohanim, at end of Bechukothai. “From now on, no prophet is permitted to originate anything [in the Torah].” Whatever [laws] the Sages have established in the nature of “a fence [around the Torah],” such as the secondary degrees of forbidden marriages37Yebamoth 21a-b. — that activity of [establishing fences] is itself a requirement of the Torah, provided only that one realizes that these [laws] are a result of a particular fence and that they are not [expressly] from the mouth of the Holy One, blessed be He, in the Torah.38In other words, the duty devolving upon the Sages to establish “fences” [i.e., safeguards against trespassing the law of the Torah] is specifically stated in the Torah, but the precise terms of these “fences” are not written. — The duty of establishing such preventive Rabbinical laws is based on the verse, ushmartem eth mishmarti (and ye shall keep My charge — Leviticus 18:30), tradition interpreting this to mean: “Make a mishmereth (a protection, a fence as a safeguard) l’mishmarti (for My commandment)” (Yebamoth 21 b).