How Can We Know the Oral Torah Is Really from Hashem, and Why Wasn't Everything Written Down?

Why should we not believe only in what is written in the Written Torah? How can we know that Hashem truly gave the Oral Torah to the people of Israel at Mount Sinai? And why did Hashem want there to be an Oral Torah at all, instead of just the Written Torah?

Here are a few verses from the Written Torah attesting to the existence of the Oral Torah, as well as the commandment of Hashem to study the Torah through the sages:
A. "These are the decrees, the statutes, and the laws which Hashem gave between Himself and the children of Israel on Mount Sinai by the hand of Moses" (Leviticus 26:46); "And you shall caution them regarding the decrees and the laws and inform them of the way they must walk and the deeds they must do" (Exodus 18:20). This means that at Mount Sinai, two Torahs were given - the Written Torah and the Oral Torah.
B. "And Hashem commanded me at that time to teach you decrees and statutes for you to do" (Deuteronomy 4:14). The Written Torah itself states that Hashem commanded Moses to teach the people the decrees and statutes orally, not just to deliver a written book of Torah.
C. "And Hashem said to Moses, 'Ascend to Me on the mountain and stay there, and I will give you the tablets of stone and the Torah and the commandment which I have written to teach them'" (Exodus 24:12). At Mount Sinai, Moses received the two tablets of the covenant, the Written Torah, and the Oral Torah. The term "commandment" in the verse indicates that not only were the tablets and the written Torah given, but also the "commandment" - explaining the Torah and practical instructions for observing the commandments. Moreover, the Written Torah attests at the end of this verse that the way to teach the people the observance of the commandments and the Torah is through guidance and instruction.
D. "And when Moses completed writing the words of this Torah in a book, until they were finished" (Deuteronomy 31:24). The Written Torah testifies that the Written Torah was delivered to the children of Israel only with the death of Moses. From this, it can be concluded that until Moses's death, the Torah was taught and transmitted orally, as no written book of Torah had yet been delivered to the people. In other words, the instruction and teaching of the Oral Torah preceded the delivery of the Written Torah.

Moses ascended Mount Sinai and remained there for 40 days and nights. During that time, Hashem taught him all the interpretations, layers, and depths of the Torah, which is the Oral Torah. During the years of wandering in the desert, Moses wrote down the Written Torah according to the word of Hashem to him. The Oral Torah, which included the rules and details, he transmitted orally to the sages of the generation, who taught and passed them on to the rest of the people.

Why Not Everything Is Written Down?

Why do we need the Oral Torah? And why did Hashem want there to be an Oral Torah at all? Why not deliver one Torah, which is only written, that includes everything?

1. You don't write a safe's code on a note. One of the answers to this question is found in a Midrash: "Hashem foresaw that idolaters would translate the Torah into Greek and claim, 'We too are Israel.' Hashem says to the nations, 'I only recognize the one who has My secrets.' What are the secrets? This is the Mishnah" (Yalkut Shimoni on Hosea).
Hashem knew that the day would come when idolaters would make false claims that Hashem had, heaven forbid, broken His covenant with the Jewish people and made a new covenant with them, giving them an addition to the original Torah. The mechanism that prevents any sensible person from believing this false claim is that the interpretation and secrets of the Torah are unknown to any people except the Jewish people, who received it by oral tradition. When Hashem made His covenant with us, He gave us the "code" to understand the Written Torah, which is often not understood, closed, and sealed. That code is the Oral Torah, ensuring the knowledge of the Torah to the children of Hashem alone - the Jewish people.

By way of metaphor, if we have a credit card in our wallet, it's likely that we wouldn't write its code on a note, so that if the wallet accidentally ends up in foreign hands, others won't have access to our bank account. We remember the code by heart only, and pass it on verbally only to those close to us whom we wish to give access, like a spouse. Similarly, Hashem gave the jewel in the crown, the Torah, only to His children. And to ensure that this precious gift would not fall into the hands of other nations, Hashem wanted the true understanding of the Torah to remain oral only.

2. Learning from the Greats. Hashem wanted the Torah to be passed down through learning from wise men to disciples, from father to son. Without an intermediary knowledgeable in the Torah, one can err in understanding the words. Therefore, the Torah was originally intended to be transmitted orally from generation to generation, through study.

3. Relevance. Another reason why the entire Torah should not be given in writing is because over the generations, changes occur, and relevant halachic rulings are needed for the changing reality. Therefore, the Oral Torah provides general rules that allow the sages of each generation to make halachic rulings on new matters in the spirit of the time. For many questions in our modern lives, there is no direct reference in the Torah, but the Oral Torah contains guiding principles by which one can deduce how to act, such as: If someone is flying on a fast day, when does the fast end for him - according to the departure country or the destination country? Is it permitted to set a Shabbat timer for the IROBOT to clean the floor during Shabbat?

In fact, the word 'halacha' itself contains the meaning of 'halacha,' which is walking in the way of the Torah alongside the dynamic and changing reality. If the entire Torah were delivered in writing, in a complete and final form, there would be no halachic response to many questions that arise with the new reality. Therefore, the Oral Torah includes within it also the rules of decision-making, through which the sages of the generation can rule the halacha.

And here is the statement of Rabbi Joseph Albo in his book 'Sefer HaIkkarim' (Article 3, Chapter 23): "It is impossible for the Torah of Hashem to be perfect in such a way that it will suffice in all times, because the continuously renewing particulars in human matters, like judgements and actions, are too numerous to be encompassed in a book. Therefore, at Sinai, Moses was given oral wholes, alluded to briefly in the Torah, so that by them the sages of each generation could bring forth the renewing particulars."

4. To Put It on the Shelf?! If the entire Torah were written, it is likely that it would find itself placed on the shelf in the library, and only glanced at when one wanted to find an answer to a specific question. The fact that the Torah is transmitted orally compels us to engage with it, labor in it, to live it and with it.

5. Index for Countless Details. When buying a new electronic device, a user manual usually accompanies it. But it will never include all the questions that can arise and all types of malfunctions. Similarly, the Written Torah includes only the general principles, like an index, and the Oral Torah comes to bridge the gap. Commands that are described in the Torah in a short and unclear sentence receive expansion and detail in the Oral Torah. For example, the Torah commands "You shall dwell in booths for seven days," but does not specify what a booth is, how to build it, and the idea behind it; the Torah commands to put on tefillin, but does not specify what tefillin look like - in what form or color, where exactly to place them, and what needs to be written in them; the Torah commands regarding a mezuzah "and you shall write them on the doorposts of your house and on your gates," but does not specify what is written in the mezuzah; the Torah commands to slaughter animals in a kosher manner, but does not specify how to do it; the Torah commands not to do work on Shabbat, but does not specify what these prohibited labors are, and dozens of other questions arise. All 613 commandments are written in the Torah, but it does not say how they are to be fulfilled. Here comes the Oral Torah, providing all the information in a full and clear manner. Without the Oral Torah, all the commandments in the Written Torah would remain sealed as a secret, and could not be fulfilled.

By the way, the simple fact that the Written Torah does not contain a detailed instruction for practical commandments, but only commands for their observance, proves that alongside the Written Torah given by Hashem, the Oral Torah was also given, expanding and explaining the written, since without the Oral Torah, there is no point in delivering the Written Torah which is sealed and not explained.