Rabbi Hershel Schachter
The Sefer Habris
On the last day of his life, Moshe Rabbeinu completed the writing of the original sefer Torah. He gave that Torah to the kohanim and instructed them to place it in the kodesh ha'kodoshim near the luchos which were in the aron. At maamad Har Sinai there was a national kabbolas haTorah, which required reading from a "sefer ha'bris." Rashi (in his commentary on Parshas Mishpatim) quotes the Mechilta saying that the "sefer ha'bris" was the Torah from Parshas Bereishis until Parshas Mishpatim. At the end of the forty years in the midbar, Moshe Rabbeinu told B'nai Yisroel that from now on the sefer ha'bris consists of the entire chamisha chumshei Torah. The Gemorah (Gittin 60a) tells us that kavod hatzibbur demands that when we read keri'as haTorah in shul we must use a complete sefer Torah which includes the entire chamisha chumshei Torah. Although leining from a klaf that included an entire chumash (e.g. Devarim) would be considered keri'a mitoch haksav (as opposed to b'al peh), nonetheless, because the bris was made with the tzibbur on the entire Torah, whenever we lein b'tzibbur we require a complete sefer ha'bris, i.e. a klaf that includes the entire chamisha chumshei Torah.
Chazal tell us (Shabbos 88a) that a second national kabbolas haTorah took place after the occasion of neis Purim. The sefer ha'bris for that second kabbolas haTorah was Megillas Esther. The Gemorah (Megillah 19a) tells us that if you have a Megillas Esther written on klaf together with other sifrei kisuvim, although the reading is considered mitoch ha'ksav, even the Megillas Esther section does not have the status of sefer ha'bris since the other seforim included therein do not have the status of sefer ha'bris. Similarly, the Rambam writes that if one combines Torah, Nevi'im, and Kesuvim on one klaf, since the Nevi'im and Kesuvim do not have the status of sefer ha'bris, even the Torah section loses its status of sefer ha'bris. Therefore, if a tzibbur leins from such a Tanach, although it would certainly be considered keri'a mitoch haksav it will constitute a violation of kavod hatzibbur. If one reads the Megillah without a minyan it would be perfectly acceptable to read from a klaf that includes other seforim as well; only betzibbur, out of kavod hatzibbur, do we require that the Megillah we read from should have the status of a sefer ha'bris.
The simple reading of the chumash might imply that for the purpose of the mitzvah of hak'hel a special sefer azarah had to be used. Some rishonim state this explicitly. Some write that on Yom Kippur as well thr special keri'as haTorah that the kohein gadol read in the Beis ha'mikdosh had to be from the sefer azarah. The Mishna (Sotah 32a) tells us that although, strictly speaking, on all other occasions one may recite the berochos on an aliyah in translation, for the keri'as haTorah of hak'hel and that of the kohain gadol on Yom Kippur, the berochos had to be recited in the original Hebrew. These two instances of keri'as haTorah are clearly Biblical mitzvos and therefore were singled out by the Mishna with respect to their berochos.
This Sifrei comments on the possuk, "me'ona Elokei Kedem" (Devarim 33:27) that at one point there was a question regarding the reading of the word: is it "mo'on" or "me'ona"? The Chachomim checked into three seforim in the azarah. Two of them read "me'ona" and the third read "mo'on", and they decided to follow the majority and established that the correct spelling of the word should be "me'ona". Why didn't the Chachomim check all of the sifrei Torah in the world to establish the correct spelling? Why did they only check the three seforim which were in the azarah? Rav Soloveitchik explained that it would appear that the halachic role of the sefer azarah is to preserve the accurate text of the chamisha chumshei Torah. For that reason only the three sifrei azarah were checked into and not all the sifrei Torah in the whole world. Just as the Rambam felt that the Aleppo Codex of Ben Asher was the official accurate text of the sefer Torah during his lifetime, the halacha considers the sifrei azarah as the official text.
The Rambam quotes from the Tosefta that when you have a melech and he has a mitzvah to write a second sefer Torah, that sefer Torah should be copied from the sefer azarah. Apparently any sefer Torah which is copied from the sefer azarah becomes itself a sefer azarah. It could well be that when the issue came up regarding the spelling of the work "me'ona" the original sefer azarah that was written by Moshe Rabbeinu was already in sheimos and the three sifrei Torah that they did check with were all copies of that sefer azarah.
This season of the year is a most auspicious time for each of us to recommit ourselves to upholding the Torah in its entirety and in a most authentic fashion, without distortions or misrepresentations. The best way to latch on to the authentic version of Torah is to become a talmid of one who has a masorah from someone else who in turn has a masroah etc., just as any sefer Torah copied from a sefer azarah gains the status of a sefer azarah, for the sake of preserving the authenticity of the Torah.
 Hilchos Sefer Torah, end of Chapter 7
 This is discussed further, at length, in sefer Ikvei Hatzon, chap. 23
 Rashi and Shita Mekubetzes, Bava Basra 14b
 Rashi ibid, and see Tosafos ibid 14a
 See Yalkut Shimoni on Parshas Vayelech, that Moshe Rabbeinu was concerned that in the future the Torah would be distorted
 Hilchos Melachim, beginning of chapter 3