The idea that teachings expounded by later sages are also the word of G‑d is illustrated by the following Talmudic account:

When Moses ascended on high, he found G‑d attaching coronets to the letters of the Torah. Said Moses to G‑d: “Master of the world! Why have You need for these?”

Said G‑d to him: “There will be a man some generations hence, whose name is Akiva the son of Joseph, and he will expound mounds upon mounds of laws from each and every tittle.”

Said Moses: “Master of the world, show him to me.”

Moses was sitting behind eight rows (of R. Akiva’s disciples) but he did not understand what they were saying, and he was despondent. Until they reached one teaching, and R. Akiva’s disciples said to him, “Master, from where do you know this?”

Said R. Akiva to them, “It is the law given to Moses at Sinai.” And Moses’ mind was eased.1

But if Moses was not cognizant of—and was even unable to understand—the teachings expounded by R. Akiva, how could these selfsame teachings be “the law given to Moses at Sinai”? By the same token, what is the meaning of the statement2 that “…even what a proficient pupil is destined to innovate, all was already said to Moses at Sinai” when that same statement refers to the new teaching as an “innovation” (chidush)—i.e., something that was not previously known?

The most basic explanation is that given by Shemoth Rabbah:

Did Moses then learn the entire Torah? It is written in the Torah: “Longer than earth is its measure, and broader than the sea”3 —and Moses learned it in forty days?! Rather, G‑d taught Moses the general principles.4

In other words, “all was given to Moses” in potential form, since all subsequent explanations, interpretations and extrapolations by the sages of later generations are extracted from the general principles given to Moses.5

Thus we have an expansion of Torah through historical time. The later biblical books of the Nevi’im (“Prophets”) and Kethuvim (“Scriptures”) are expositions of the laws and principles transcribed by Moses in the Chumash If Moses was not cognizant of the teachings expounded by R. Akiva, how could these selfsame teachings be ‘the law given to Moses at Sinai’? (“Five Books”).6 The Mishnah codifies the laws extracted from the biblical text; the Talmud extrapolates laws and principles from Mishnah; the rishonim (“early commentaries”) expound and deduce from the Talmud; and the acharonim (“later commentaries”) expound and deduce from the rishonim. Each generation and era reveals new facets and genres of Torah learning, yet all was “already said to Moses at Sinai” in potential form.

Shaloh takes this a step further, explaining how also the “safeguards” and “ordinances” instituted by the sages (categories 4 and 5 in Maimonides’s enumeration cited above) are included within the divine revelation at Sinai. Shaloh notes that the blessing recited before studying Torah concludes with the words “Blessed are You, G‑d, who gives the Torah” (nothein hatorah)—in the present tense:

In truth, G‑d has already given us the Torah (at Mount Sinai); yet we refer to G‑d as one who still perpetually gives the Torah. This matter requires some elaboration.

It is written: “These words G‑d spoke to your entire congregation at the mountain… a great voice which did not cease.”7 Rashi explains the meaning of the words “did not cease” (velo yasaf) in accordance with the translation by Onkelos—it did not stop, for it is a powerful voice which endures forever. Rashi also offer a second interpretation of the words velo yasaf—“it did not any more,” i.e., that G‑d did not again speak so openly and publicly as He did at Sinai.

There is a profound significance in these two interpretations, as they are simultaneously true. The divine voice spoke the Torah at Sinai and “did not any more,” as all the subsequent laws and edicts instituted by the sages throughout the generations were not explicitly commanded by G‑d. At the same time “it did not cease,” for everything was included, in potential form, within that voice. It is only that “for everything there is a time and season,”8 and the time had not yet come for that potential to emerge into actuality; for that depends on the initiative of those down here below, in accordance with their nature and their abilities, and in accordance with the qualities of the souls of each generation. Following the revelation at Sinai, the sages of each generation were roused to actualize from that potential in accordance with the time and season. Thus, the sages did not invent anything from their own minds, G‑d forbid, but rather actualized the divine intent.9

Neither of these explanations, however, fully explains the Talmud’s use of the term chidush—which literally means “new thing” or “innovation”—when it declares that “even what a proficient pupil is destined to innovate was already said to Moses at Sinai.”10 Indeed, the concept or ruling is “new” in the sense that is has been newly discovered and revealed, having previously existed solely in potential form. Nevertheless, the true meaning of the term chidush is something that is entirely new.

This prompts the Rebbe to suggest another, deeper explanation for how the “innovations” of later Torah scholars were “already said at Sinai.” The Rebbe’s explanation is predicated on the principle, widely discussed in Kabalah and in chassidic teaching, that the souls of Israel are rooted in the deepest recesses of the “mind” of G‑d. The source of this principle is the midrashic teaching A concept conceived by the soul of the Torah scholar becomes part of the Torah’s inception in the mind of G dthat both the Torah and the souls of Israel preceded the creation of the world. The Midrash then asks, “Still, I do not know which preceded which?” and concludes: “The thought of Israel preceded everything.”11

Time is part and parcel of the natural creation,12 meaning that all which “precedes” creation exists beyond the realm of time. Within historical time, the Torah unfolds from the general to the particular and from potential to actuality; Moses receives the “general principles” at Sinai, and the “proficient pupils” of each generation extract from these principles specific ideas, laws and applications. But all parties to this process—G‑d, the soul of the Torah scholar, and the Torah itself—are “pre-creation” realities. This means that the dynamic between them also transpires beyond historical time—indeed, beyond time itself. On this level, the “new” concept is conceived by soul of the Torah scholar, as that soul is rooted within G‑d, Giver of the Torah, making the concept an integral part of Torah from the Torah’s very inception in the mind of G‑d.13

The Oral Torah, then, is the product of the collaboration of divine revelation and human intellect. This collaboration takes place on two levels. On the exoteric level, in a process unfolding through linear time, the human intellect unpacks concepts and laws from their potential state within the divinely revealed general principles. On a deeper, esoteric level, the process runs in the reverse: the soul innovates in Torah using the human intellect as its tools, but because it is rooted in the divine essence, wherein the past and the future are undifferentiated, it in effect imparts these "innovations" retroactively to the divine communication at Sinai.14