The pasuk itself establishes that Israel is bound not only to the written verdict but to 'all their instructions,' indicating from the outset that the transmission system Hashem established was not confined to a fixed written text (Devarim 17:10-11).
The Yerushalmi teaches that everything a veteran student will ever innovate before his teacher — mikra, mishnah, talmud, and aggadah alike — was already said to Moshe at Sinai, meaning the Oral Torah was never meant to be a static document but an unfolding transmission rooted in a single original moment (Jerusalem Talmud Peah 2:4).
The Bavli in Temurah describes how, after Moshe's death, three thousand halachot were actually forgotten and could not be retrieved even through prophecy, since Yehoshua and later Shmuel both responded that the Torah 'is not in Heaven' and that no prophet may now add anything — showing that even orally transmitted law, once fixed by decree, could be lost, which bears directly on why a living process of transmission matters rather than mere transcription (Temurah 16a).
The Rambam frames the entire structure of Torah and mitzvah on the fact that the mitzvot were given to Moshe at Sinai 'with their explanation,' and that this explanation — called the Oral Torah — was not written but commanded to the elders, Yehoshua, and all of Israel, establishing that the explanatory layer of Torah was from the start meant to travel through a person-to-person chain rather than ink (Mishneh Torah, Transmission of the Oral Law 1:1-11).
The Gemara in Gittin records the actual machlokes about the proportion of written to oral Torah, with Rabbi Elazar holding that the majority was transmitted in writing and only a minority orally, against Rabbi Yochanan who holds the reverse — and it further derives from the double language 'write for yourself' together with 'for on the basis of these words' that there are matters you may not say in writing and matters you may not write down, establishing a formal distinction between what belongs to each domain (Gittin 60b).
The Kuzari observes that even the plain text of the Chumash requires several classes of received tradition — vocalization, cantillation, division of verses, and masoretic transmission — to be read correctly at all, and that the hidden dimension of Torah, being broader than its words, could never be relied upon except through the Oral Torah (Kuzari 3:35).
The Maharal in Tiferet Yisrael takes up the question directly — why was not everything given in writing — and explains, following the derivation in Gittin, that there are matters you may not state in writing and matters you may not state orally, and that the Oral Torah's very nature as oral is bound up with why it could not have been committed to writing in the same form as the mikra (Tiferet Yisrael 68, and further at Tiferet Yisrael 68:8 and Tiferet Yisrael 69); he adds that Moshe was told the mikra would be given in writing while the aggadah, mishnah, and gemara would remain oral specifically because these oral teachings would serve to distinguish Israel from the nations who would later seize the written text, and separately that had all such material been written into the Torah itself, learners of lesser capacity could not have managed it, so the Written Torah carries the principles while the Oral Torah was entrusted to the great sages to transmit to each person according to his capacity.
The Netivot Olam likewise discusses how halachic rulings are properly transmitted 'from their mishnah,' tying the authority of oral teaching to a living understanding rather than to the bare written formula (Netivot Olam, Netiv Hatorah 15).
The Maharal's own aggadic commentary develops the distinction between writing and speech on a conceptual level: writing conveys an idea through a visual-intellectual form while speech requires expression from the mouth, so that the completeness of the Written Torah stands in contrast to the oral mode, which is necessarily conveyed part by part even when the whole is recited — and on this basis Torah sheba'al peh should not be written down (Chiddushei Aggadot, Sanhedrin 22, Chiddushei Aggadot, Gittin 60, Chiddushei Aggadot, Gittin 58, and Maharal (Chiddushei Aggadot, Sanhedrin 21)).
Daas Torah develops this same point in the other direction: just as the written may not be stated orally, the oral may not be committed to writing, because the Torah must also live within a person in oral form, woven into his inner being, so that the Written Torah itself issues forth as the product of an indwelling Oral Torah — the two are interlocked and dependent on one another (Daas Torah (Rav Yerucham Levovitz)).
Shiurei Daas explains the purpose behind this structure: the Oral Torah was given alongside the Written Torah precisely because only a living tradition, handed from person to person and generation to generation, can clarify the Torah's hidden and wondrous matters, something a fixed text alone cannot do (Shiurei Daas 1 p. 68).
The Or HaChaim likewise responds to the implicit question of why Hashem would conceal wisdom from His servants rather than spelling everything out in writing, answering that these matters simply cannot be contained in a book, since even a teacher's full transmission to a single student could not be captured by filling the skies with parchment (Or HaChaim on Shemot 31:13).
A Chassidic source situates the oral dimension of Torah study itself within this same picture, explaining that speech was necessary in the giving of the Torah because Torah, likened to fire, must move from a hidden state into revealed expression, and concludes that this is why speech in Torah is required even when forgetting is not the operative concern (Maamarim Melukatim, ש״פ תולדות).
Nedarim brings a related tradition that the Torah was originally given only to Moshe and his descendants, and that Moshe himself, acting with generosity, gave it over to the rest of Israel — framing the transmission of Torah, written and oral alike, as fundamentally an act of handing over rather than simple publication (Nedarim 38a).
The Radbaz discusses the angels' objection to giving the Torah to mortals and resolves it by distinguishing between a spiritual, letter-undivided reading of the Torah as Hashem's names and the physical reading divided into words dealing with human affairs — a distinction that itself depends on an received, non-written layer of understanding (Teshuvot HaRadbaz Volume 3 1068}).
Mishneh Halachos draws the line sharply: the Written Torah was disclosed broadly to all, while the Oral Torah was transmitted only orally, and the prohibition against writing applies specifically to that oral layer and not to the Written Torah (Mishneh Halachos 5:172).
Other sources on the sheet reflect on the broader character of imitating Hashem's ways and on the nature of halachic reasoning and its metaphysical weight, which, while not focused on the writing question itself, round out the picture of why Torah study and transmission carry the form that they do (Sefer HaMitzvot, Positive Commandments 8, Tanya, Part I; Likkutei Amarim 5, Sefer HaIkkarim, Maamar 3 3:9, and Maharal, Be'er HaGolah 6).
